Every surname on the atlas alongside the form it was written in before English spelling got to it. Murphy was Ó Murchadha. Smith was Mac Gabhann. The English version is a clerk's best guess at a sound; this is the name itself.
| Surname | In Irish | What it means | Homeland |
|---|---|---|---|
| Adams | Mac Ádhaimh | son of Adam | Antrim, Armagh, Cavan |
| Agnewalso O'Gnyw | Ó Gnímh | descendant of Gníomh, 'action' | Antrim, Down |
| Ahernalso Aherne, Hearn | Ó hEachthighearna | descendant of Eachthighearna, 'lord of horses' | Cork, Clare |
| Archer | Áirséir | the bowman | Kilkenny |
| Aylward | Aighleart | æthel-weard, 'noble guardian' | Waterford, Kilkenny |
| Bannonalso Bannan, Banan, Banim, O'Bannon | Ó Banáin | descendant of Banán, a diminutive of bán, ‘white’ | Offaly, Mayo, Fermanagh |
| Barrett | Bairéid | possibly 'quarrelsome' (baraud) | Mayo, Cork |
| Barryalso de Barry | de Barra | from Barri in Wales | Cork |
| Beattiealso Beatty | Biadhtach (source) | from Bartholomew — or Irish biadhtach, 'public hospitaller' | Antrim, Fermanagh |
| Begleyalso Bagley, Bigley, O'Begley | Ó Beaglaoich | descendant of the little hero, from beaglaoch | Donegal, Cork |
| Behanalso O'Behan, Beahan | Ó Beacháin | descendant of Beachán — from beach, 'bee' | Offaly, Laois |
| Berginalso Bergen, Berrigan, O'Havergan | Ó hAimheirgin | descendant of Aimhirgin, 'wondrous birth' | Offaly, Laois |
| Berminghamalso Birmingham | Mac Fheorais | from Birmingham, England | Galway, Kildare |
| Blake | de Bláca | le blac — 'the black-haired' | Galway, Mayo |
| Bodkin | Boidicín | a nickname from a short dagger | Galway |
| Bolandalso Bolan, Bowland, O'Boland | Ó Beólláin | descendant of Beóllán | Sligo |
| Boycealso Bowe, Bowes, Boyes, O'Boyce, Bogue, Bowie | Ó Buadhaigh | descendant of Buadhach, ‘victorious’; or Norman ‘de Bois’, of the wood | Donegal, Kilkenny, Cork |
| Boylanalso O'Boylan, Boyland | Ó Baoighealláin | descendant of Baoigheallán | Monaghan |
| Boylealso O'Boyle | Ó Baoighill | descendant of Baoigheall, 'vain pledge' | Donegal |
| Bradleyalso O'Brollaghan, O'Brallaghan, Brollaghan | Ó Brolcháin | descendant of Brolachán, a diminutive of Brólach | Tyrone, Derry / Londonderry, Donegal, Mayo |
| Bradyalso MacBrady | Mac Brádaigh | son of Brádach, 'spirited' | Cavan |
| Branaganalso Brannigan, Branigan | Ó Branagáin | descendant of Branagán — from bran, a raven | Derry / Londonderry |
| Breenalso O'Breen, Bruen | Ó Braoin | descendant of Braon, 'sadness' or 'sorrow' | Westmeath, Roscommon, Kerry |
| Brennanalso O'Brennan | Ó Braonáin | descendant of Braonán, 'little drop / sorrow' | Kilkenny, Roscommon, Sligo |
| Breslinalso O'Breslin, Bresland | Ó Breisleáin | descendant of Breasal — the meaning of the personal name is not securely known | Donegal, Fermanagh |
| Broderickalso Brouder, Broder, Brothers | Ó Bruadair | descendant of Bruadar — from the Norse personal name Broddr | Kilkenny, Galway, Cork |
| Broganalso O'Brogan, MacBrogan | Ó Brógáin | descendant of Brógán — probably from bróg, 'shoe' | Mayo, Donegal |
| Brophyalso O'Brophy, Brophie | Ó Bróithe | descendant of Brothe | Laois, Kilkenny, Carlow |
| Brosnanalso Brosnahan | Ó Brosnacháin | of Brosna — the river and village in Kerry | Kerry |
| Buckleyalso O'Buckley | Ó Buachalla | descendant of Buachaill, 'the herdsman' | Cork, Kerry |
| Bulgeralso Bolger, Boulger, O'Bolger | Ó Bolguidhir | descendant of Bolgodhar — perhaps a nickname | Wexford |
| Burkealso Bourke, de Burgh | de Búrca | from de Burgh — 'of the borough' | Galway, Mayo |
| Butler | de Buitléir | le botiler — the (chief) butler of Ireland | Kilkenny, Tipperary |
| Byrnealso O'Byrne, Beirne | Ó Broin | descendant of Bran, 'raven' | Wicklow, Dublin |
| Caffertyalso MacCafferty, Cafferkey | Mac Eachmharcaigh | son of Eachmharcach, 'horse-rider' | Donegal, Mayo |
| Cagneyalso O'Cagney, Caney | Ó Caingne | descendant of Caingne — from caingean, 'a legal dispute'; an advocate's name | Cork |
| Cahillalso O'Cahill, Cahil | Ó Cathail | descendant of Cathal — cath, 'battle', with either 'rule' or 'great' | Galway, Kerry, Tipperary |
| Callanalso Callen | Ó Cathaláin | descendant of Cathalán, 'little battle-mighty one' | Louth, Monaghan, Armagh |
| Campbell | Mac Cathmhaoil (adopted) | cam beul, 'crooked mouth' | Antrim, Down, Tyrone |
| Canavanalso O'Canavan, Kinavan, Kinevan | Ó Ceanndubháin | descendant of Ceanndubhán, 'the dark-headed one' | Galway, Cork |
| Cannonalso Canon, MacCannon, Cannan | Mac Canann | son of Cana, 'a whelp' or wolf cub | Donegal |
| Cantwell | Cantual | from Kentwell, Suffolk | Kilkenny, Tipperary |
| Cantyalso County, O'Canty | Ó an Cháinte | descendant of the satirist, from cáinteach | Cork, Kerry, Limerick |
| Carewalso Carru, Carrew | de Carrún | from Carew in Pembrokeshire — a place name, 'the fort by the ford' | Cork, Tipperary |
| Careyalso Cary, O'Carey, Keary | Ó Ciardha / Ó Cearaigh | descendant of Ciardha, 'the dark one' — among several distinct roots | Kildare, Mayo, Cork |
| Carmodyalso Kermody | Ó Cearmada | descendant of Cearmaid — a very ancient personal name | Clare, Kerry, Limerick |
| Carolanalso O'Carolan, Carrolan | Ó Cearbhalláin | descendant of Cearbhallán, 'little Cearbhall' | Cavan, Monaghan, Tyrone, Donegal |
| Carrollalso O'Carroll | Ó Cearbhaill | descendant of Cearbhall, 'fierce in battle' | Offaly, Tipperary, Louth |
| Cartyalso Carthy, McCarty | Ó Cárthaigh | descendant of Cárthach, 'loving' | Roscommon, Tipperary, Clare |
| Caseyalso O'Casey | Ó Cathasaigh | descendant of Cathasach, 'vigilant in war' | Cork, Dublin, Limerick |
| Cassidyalso O'Cassidy | Ó Caiside | descendant of Caiside, 'curly-haired' | Fermanagh |
| Clancyalso MacClancy, Glancy | Mac Fhlannchaidh | son of Flannchadh, 'the red warrior' | Clare, Leitrim |
| Clarkealso Clark, O'Clery, Cleary | Ó Cléirigh | descendant of the cleric — possibly Europe's oldest surname (916 AD) | Donegal, Cavan, Galway |
| Cliffordalso de Clifford, Cluvane, Clovan | Ó Clúmháin | descendant of Clúmhán, from clúmhach, ‘hairy’; or Norman ‘de Clifford’, of Clifford in Herefordshire | Sligo |
| Clohessyalso Cloghessy, O'Clohessy, O'Cloghessy | Ó Clochasaigh | descendant of Clochasach | Clare, Limerick |
| Codyalso Codd | Mac Óda | son of Odo | Kilkenny, Wexford |
| Coffeyalso O'Coffey, Cowhey | Ó Cobhthaigh | descendant of Cobhthach, 'victorious' | Westmeath, Longford, Cork |
| Colemanalso Colman, O'Clumhain | Ó Colmáin / Ó Clumháin | descendant of Colmán, 'little dove' — from Latin columba | Sligo, Cork, Tipperary |
| Colganalso O'Colgan, Colgin | Ó Colgáin | descendant of Colga — from colg, 'sword' or 'thorn' | Offaly, Clare |
| Collinsalso O'Collins | Ó Coileáin | descendant of Coileán, 'young hound / whelp' | Cork, Limerick |
| Comerford | Comartún | from Comberford, Staffordshire | Kilkenny, Waterford |
| Comiskeyalso Cumiskey, Cummiskey, Comaskey | Mac Cumascaigh | son of Cumascach, 'the confuser' or 'mixer' | Monaghan, Cavan |
| Concannonalso Concanon, Conceanainn | Ó Concheanainn | descendant of Cú Cheanainn, 'fair-headed hound' | Galway |
| Condon | Condún | de Caunteton — from Welsh Marches | Cork, Tipperary |
| Conlanalso Conlon, Connellan | Ó Conalláin / Ó Caoindealbháin | descendant of Conallán — a diminutive of Conall | Roscommon, Tyrone, Meath |
| Conneelyalso MacConneely, Kineally, Conneally | Mac Conghaile / Ó Conghaile | son of Conghal — 'hound' and 'valour' | Galway, Mayo |
| Conneryalso Conery, O'Connery | Ó Conaire | descendant of Conaire, 'keeper of the hound' | Waterford, Wexford |
| Connollyalso Connelly, O'Connolly | Ó Conghalaigh | descendant of Conghalach, 'valiant as a hound' | Monaghan, Galway, Meath |
| Conroyalso Conry, Mulconry, O'Mulconry | Ó Maolchonaire | descendant of Maolchonaire, 'follower of Conaire' | Roscommon, Clare |
| Considine | Mac Consaidín | son of Constantine | Clare |
| Conwayalso O'Conway, Conboy, Conaboy | Ó Connmhaigh | descendant of Connmhach | Clare, Sligo, Galway |
| Cooganalso Cogan, MacCoogan | Ó Cuagáin / Mac Cogadháin | descendant of Cuagán (Kilkenny line); or son of Cogadhán, from Cú Chogaidh, 'war-hound' (Leitrim line) | Kilkenny |
| Cooneyalso O'Cooney, Coonan, Coony | Ó Cuana | descendant of Cuana | Tyrone, Galway, Clare |
| Corbettalso Corbet | Corbaid | 'son of Corbet' — from French corbeau, a raven | Meath, Offaly |
| Corcoranalso Corkery | Ó Corcráin | descendant of Corcrán, 'purple-faced' | Tipperary, Offaly, Fermanagh |
| Cormackalso Cormac, O'Cormack, Cormick | Ó Cormaic | descendant of Cormac — 'son of Corb', or charioteer | Derry / Londonderry, Cork |
| Corriganalso O'Corrigan, Carrigan | Ó Corragáin | descendant of Corragán | Fermanagh, Monaghan |
| Costelloalso Costelloe | Mac Oisdealbhaigh | son of Oisdealbh — the first Norman family to take a 'Mac' | Mayo, Galway |
| Cotteralso MacCotter | Mac Coitir | son of Oitir — the Norse Ottar | Cork |
| Coughlanalso Coghlan, Coughlin, Coghlin | Ó Cochláin / Mac Cochláin | descendant or son of Cochlán — from cochall, 'cloak' or 'hood' | Cork, Offaly |
| Coynealso O'Coyne, Kyne, Barnacle | Ó Cadhain | descendant of Cadhan — a personal name from the barnacle goose | Galway, Mayo |
| Creaghalso Craugh | Craobhach | 'of the branch' — from craobh, a branch | Clare, Limerick |
| Creanalso Creane, Crane | Ó Carráin | descendant of Carrán — from carra, a spear | Kerry, Cork |
| Creedonalso Creed, O'Creedon | Ó Críodáin | descendant of Críodán | Cork |
| Creminalso Cremen, Crimmins, Crimmeen, Cremeen, O'Cremin | Ó Cruimín | descendant of Cruimín, a diminutive of crom, ‘bent’ | Cork, Kerry, Limerick |
| Cronanalso O'Cronan, Kronane | Ó Crónáin | descendant of Crónán — a pet form of Crón, 'dark' or 'swarthy' | Laois |
| Croninalso O'Cronin | Ó Cróinín | descendant of Crónín, 'little dark-yellow one' | Cork, Kerry |
| Crowleyalso O'Crowley | Ó Cruadhlaoich | descendant of Cruadhlaoch, 'hard hero' | Cork |
| Culhanealso Callaine, Clahane | Ó Cathláin | descendant of Cathalán, 'battle-mighty' | Limerick |
| Cullenalso O'Cullen, Cullinane | Ó Cuilinn | descendant of Cuileann, 'holly' | Wicklow, Wexford, Kildare |
| Cullotyalso Cullity, O'Collitie | Ó Codlata | descendant of Codladh, 'sleep' | Kerry, Cork |
| Cumminsalso Cummings, Cummin, Cumin, Comyn, Comyns | Ó Cuimín | descendant of Cuimín, a diminutive of cam, ‘bent’; or the Norman Comyn | Sligo, Westmeath, Roscommon |
| Cunninghamalso Cunnigan, Kinnegan, Connigan, MacCunnigan | Ó Connagáin | descendant of Connagán, a diminutive of Conn | Sligo, Galway |
| Curranalso O'Curran, Corran, Currane | Ó Corráin | descendant of Corrán | Donegal, Waterford, Kerry, Leitrim |
| Curtinalso Curtayne, MacCurtain | Mac Cairteáin | a softened form of Mac Cartáin | Cork, Kerry, Limerick |
| Cusack | Ciomhsóg | from Cussac in Guyenne | Meath, Clare |
| Dalyalso O'Daly, Daley | Ó Dálaigh | descendant of Dálach, 'of the assembly' | Westmeath, Cork, Galway |
| Danaheralso Dannaher, Danagher, Daniher, Donaher, Deneher, Donogher | Ó Duineachair | descendant of Duineachar, ‘man-loving’ | Tipperary, Limerick |
| Darcyalso D'Arcy | Ó Dorchaidhe / d'Arcy | descendant of Dorchaidh, 'dark one' — or from Arcy in France | Galway, Meath, Wexford |
| Davorenalso O'Davoren, Davern, Davoran | Ó Duibhdábhoireann | descendant of Dubhdábhoireann, 'black of the two Burrens' | Clare, Tipperary |
| Deasyalso Deasey, Deacy | Déiseach | 'of the Déise' — a man of the Déise people | Waterford, Cork |
| Deeganalso Deighan, Digan, Diggin, Deegin, Duigan, O'Deegan | Ó Duibhginn | descendant of Dubhcheann, ‘black head’ | Galway, Clare, Wexford, Offaly, Laois, Kerry |
| Delaneyalso Delany | Ó Dubhshláine | descendant of Dubhshláine, 'dark one of the Slaney' | Laois, Kilkenny |
| Dempseyalso O'Dempsey | Ó Díomasaigh | descendant of Díomasach, 'the proud' | Laois, Offaly |
| Dennehyalso Denehy, Danahy | Ó Duineachdha | descendant of Duineachaidh — read as 'humane' | Cork |
| Dennisalso Denis, Dennison, Denison, Denson | Ó Donnghusa | descendant of Donnghus, ‘brown choice’ | Cork, Waterford |
| Desmond | Ó Deasmhumhnaigh | 'descendant of the Desmond man' (native of south Munster) | Cork |
| Devaneyalso Devany, O'Devaney, Devanny | Ó Duibheamhna | descendant of Dubheamhain — dubh, 'black', with Eamhain, the old name of Navan Fort | Armagh, Down |
| Devereuxalso Deveraux | Deabhrús | from Évreux in Normandy | Wexford |
| Devinealso Devin, O'Devine, Devinne | Ó Daimhín | descendant of Daimhín | Fermanagh |
| Devlinalso O'Devlin | Ó Doibhilin | descendant of Doibhilean | Tyrone, Derry / Londonderry |
| Diamondalso Dimond, Diamon, O'Diamond | Ó Diamáin | descendant of Diamán, more correctly Díomán, a diminutive of the personal name Díoma | Derry / Londonderry, Antrim |
| Díazalso Diaz, Dias, Díez | — (Spanish name; Diaz in English) | 'son of Diego' — a patronymic from the Visigothic period; El Cid himself was Rodrigo Díaz de Vivar, son of Diego | Dublin, Cork, Kerry |
| Dillon | Diolún | from de Leon | Westmeath, Roscommon, Mayo |
| Dinneenalso Dineen, O'Dinneen, Denning | Ó Duinnín | descendant of Duinnín, a diminutive of donn, 'brown' | Cork |
| Diskinalso O'Diskin, Duskin | Ó Díscín | descendant of Díscín, a diminutive of díosc (apparently not a personal name) | Sligo, Galway |
| Dohertyalso O'Doherty, Dougherty, Docherty | Ó Dochartaigh | descendant of Dochartach, 'the hurtful' | Donegal, Derry / Londonderry |
| Dolanalso O'Dolan | Ó Dubhláin | descendant of Dobhailen | Roscommon, Galway, Cavan |
| Doneganalso O'Donegan, Dungan | Ó Donnagáin | descendant of Donnagán — a diminutive of donn, 'the dark one' or 'brown' | Cork, Tipperary, Monaghan |
| Donnellanalso O'Donnellan, Donnellon | Ó Domhnalláin | descendant of Domhnallán, a diminutive of Domhnall, 'world-ruler' | Galway, Roscommon |
| Donnellyalso O'Donnelly | Ó Donnghaile | descendant of Donnghal, 'brown valour' | Tyrone |
| Donovanalso O'Donovan | Ó Donnabháin | descendant of Donndubhán, 'dark brown-haired chief' | Cork, Limerick |
| Dooleyalso O'Dooley, Dowley | Ó Dubhlaoich | descendant of Dubhlaoch — dubh, 'dark', and laoch, 'warrior' | Offaly, Laois |
| Doranalso O'Doran | Ó Deoráin | descendant of Deoradhán, 'the exile, the pilgrim' | Wexford, Laois, Down |
| Dorganalso Dargan, Dergan | Ó Deargáin | descendant of Deargán, 'red' | Cork |
| Dowlingalso O'Dowling, Doolin | Ó Dúnlaing | descendant of Dúnlang | Laois, Cork, Kerry |
| Downeyalso O'Downey, Muldowney | Ó Duibheanaigh / Ó Maoldomhnaigh | descendant of Duibheanach — or, for the second sept, 'devotee of the church' | Galway, Cork, Kerry |
| Doylealso O'Doyle, MacDowell | Ó Dubhghaill | descendant of Dubhghall, 'dark foreigner' — a Viking | Wexford, Wicklow, Dublin |
| Drennanalso Drinan, Drinane, Dreinan, O'Drennan | Ó Draighneáin | descendant of Draighneán, ‘blackthorn’ | Galway, Clare, Cavan, Westmeath, Laois, Kilkenny |
| Duanealso Dwane, Devane, Downes | Ó Dubháin | descendant of Dubhán, 'black' | Meath, Cork, Galway, Limerick |
| Duffalso O'Duff, Duffin, MacElduff | Ó Duibh | descendant of Dubh, 'the black' or 'dark' | Laois |
| Duffyalso O'Duffy, Duhig | Ó Dubhthaigh | descendant of Dubhthach, 'the dark one' | Monaghan, Donegal, Roscommon |
| Dugganalso Dugan, O'Duggan | Ó Dubhagáin | descendant of Dubhagán, 'the little dark one' | Cork, Galway |
| Duignanalso Duigenan, Dignan, Deignan, Dignam, Duignam, O'Duignan | Ó Duibhgeannáin | descendant of Dubhgeannán, a diminutive of Dubhcheann, ‘black head’ | Roscommon |
| Dunnealso Dunn, O'Dunne | Ó Doinn | descendant of Donn, 'the brown-haired' (or the god of the dead) | Laois |
| Durcanalso Durkin, Durkan, Gurkin | Mac Dhuarcáin | son of Duarcán | Sligo, Mayo |
| Dwyeralso O'Dwyer, Dwire, O'Deere, Deere, Diver | Ó Dubhuidhir | descendant of Dubhodhar, ‘black Odhar’ | Tipperary, Donegal |
| Earlyalso Earley, Eardley | Ó Maolmhochóirghe | descendant of Maolmhocheirghe, ‘chief of early rising’ | Leitrim, Cavan, Roscommon, Sligo, Donegal |
| Eganalso Keegan, MacEgan | Mac Aodhagáin | son of little Aodh | Galway, Tipperary, Offaly |
| Enrightalso MacEnright, Enraght, Inright | Mac Ionnrachtaigh | son of Ionnrachtach, 'unlawful' | Limerick, Clare |
| Esmonde | Easmonn | east-mund, 'grace-protector' | Wexford |
| Fahertyalso O'Faherty | Ó Fathartaigh | descendant of Fathartach | Galway |
| Fahyalso Fahey, Vahey | Ó Fathaigh | descendant of Fathadh, 'foundation / green field' | Galway |
| Fallonalso O'Fallon, Falloon | Ó Fallamhain | descendant of Fallamhan, 'leader' | Roscommon, Galway |
| Farleyalso Farrelly, O'Farrelly | Ó Faircheallaigh | descendant of Faircheallach | Cavan |
| Fearonalso Feran, Feron, Ferran, Fearen, Fearn, Fern, Farran, Farren, O’Feran | Ó Fearáin | descendant of Fearán, a diminutive of fear, ‘a man’, or a pet form of Fearadach | |
| Feeneyalso Feeny, Finney | Ó Fiannaidhe | descendant of Fiannaidhe, 'soldier' | Sligo, Galway |
| Fennellyalso Finnelly, Finlay | Ó Fionnghalaigh | descendant of Fionnghalach, 'fair-valorous' | Tipperary, Kilkenny |
| Ferguson | Mac Fearghusa | son of Fearghus, 'man-strength' | Antrim, Down |
| Finnalso O'Finn, Fynn | Ó Finn | descendant of Fionn, 'fair' | Sligo, Monaghan, Galway |
| Finneganalso Finegan | Ó Fionnagáin | descendant of Fionnagán, 'little fair one' | Cavan, Monaghan, Galway |
| Finnertyalso Finaghty, Fenaghty | Ó Fionnachta | descendant of Fionnachta, 'fair-snow' | Roscommon, Galway |
| Finucanealso Finnucane, O'Finucane | Ó Fionnmhacáin | descendant of Fionnmhacán, ‘fair little son’ | |
| Fitzgeraldalso FitzGerald | Mac Gearailt | fitz Gerald — son of Gerald (of Windsor) | Kildare, Kerry, Limerick |
| Fitzgibbonalso Fitzgibbons, Gibbons | Mac Giobúin | son of Gibbon — Norman French fitz, 'son of', and a pet form of Gilbert | Limerick, Mayo |
| Fitzpatrick | Mac Giolla Phádraig | son of the devotee of Patrick | Laois, Kilkenny |
| Fitzsimonsalso Fitzsimmons, FitzSimons | Mac Síomóin | son of Simon | Meath, Cavan, Dublin |
| Flanaganalso O'Flanagan, Flanigan | Ó Flannagáin | descendant of Flannagán, 'little red one' | Roscommon, Fermanagh, Offaly |
| Flanneryalso O'Flannery | Ó Flannabhra | descendant of Flannabhra, 'red-eyebrows' | Limerick, Mayo |
| Fleming | Pléimeann | 'the Fleming' — from Flanders | Meath, Louth |
| Flynnalso O'Flynn, Flinn | Ó Floinn | descendant of Flann, 'ruddy' | Cork, Roscommon, Antrim |
| Fogartyalso O'Fogarty, Gogarty | Ó Fógartaigh | descendant of Fógartach, 'the banished' or 'proclaimed' | Tipperary |
| Foleyalso O'Foley | Ó Foghladha | descendant of Foghlaidh — 'the plunderer' | Waterford, Kerry, Cork |
| Fordealso Ford, MacConsnave, Foran | Mac Conshnámha / Mac Giolla na Naomh / Ó Fuaráin | three Irish names all mistranslated as 'ford': 'son of the swimming-hound' (Leitrim), 'son of the devotee of the saints' (Galway), 'descendant of Fuarthán, the cold one' (Cork) | Leitrim, Galway, Cork |
| Frenchalso ffrench | de Fréins | 'the Frenchman' | Galway, Roscommon, Wexford |
| Frielalso Freel, O'Freel | Ó Firghil | descendant of Fearghal, 'super-valour' | Donegal |
| Furlong | Furlong | from the furrow-length of a ploughed field | Wexford |
| Gaffneyalso Gawney | Ó Gamhna | descendant of Gamhain, 'calf' | Tipperary, Kilkenny, Sligo |
| Gallagheralso Gallaher, O'Gallagher, Gallacher, Gallogher, Gollagher | Ó Gallchobhair | descendant of Gallchobhar, 'foreign help' | Donegal |
| Galvin | Ó Gealbháin | descendant of Gealbhán, 'bright-white' | Kerry, Clare, Cork |
| Ganleyalso Ganly, Gantley | Mag Sheanlaoich | son of the old hero, from seanlaoch | Roscommon, Leitrim |
| Garrahyalso MacGarry, Garry, Garrihy | Mag Fhearadhaigh | son of Fearadhach, 'manly' | Roscommon, Tyrone, Antrim |
| Garveyalso O'Garvey | Ó Gairbhith | descendant of Gairbhith, 'rough peace' | Armagh, Down, Mayo |
| Gaughanalso Gavaghan, Gavigan, Gahan | Ó Gáibhtheacháin | descendant of Gáibhtheachán, 'plaintive' | Mayo, Sligo |
| Gavinalso Gavan, Gaven, O'Gavin | Ó Gábháin | descendant of Gábhadhán, a diminutive of gábhadh, ‘want, need, danger’ | Cork |
| Gaynoralso Gainer, Magenor, Geanor | Mag Fhionnbhairr | son of Fionnbharr, 'fair-head' | Longford |
| Geogheganalso MacGeoghegan, Gahagan, Gagan | Mag Eochagáin | son of Eochagán, from Eochaidh — a name built on each, 'horse' | Westmeath |
| Geraghtyalso MacGeraghty, Gearty, Gerity | Mag Oireachtaigh | son of Oireachtach, 'member of an assembly' | Roscommon, Galway |
| Gibneyalso O'Gibney, Giboney | Ó Gibne | descendant of Gibne, ‘hound’ | Meath, Cavan |
| Gillalso McGill, Gilbride | Mac an Ghoill | son of the foreigner | Mayo, Donegal, Down |
| Gilliganalso MacGilligan, Gilgan | Mac Giollagáin | son of Giollagán — 'youth, lad' | Derry / Londonderry, Antrim, Donegal |
| Gilsenanalso Gilshenan, Gilshenon, Gelshinan, MacGilsenan | Mac Giolla Seanáin | son of the servant of St Senan | Meath, Cavan, Tyrone |
| Gleesonalso Gleason, Glissane | Ó Glasáin | descendant of Glasán — from glas, grey | Tipperary, Limerick, Cork, Kilkenny |
| Glennonalso Glenane, Maglennon, MacGlennon | Mag Leannáin | son of Leannán, a diminutive of leann, ‘a cloak’ | |
| Glynnalso McGlynn, MacGlynn, MacGlin, Glinn | Mag Fhloinn | son of Flann, ‘ruddy’ | |
| Gormanalso O'Gorman, MacGorman | Mac Gormáin | son of Gormán, 'the noble dark one' | Laois, Clare, Monaghan |
| Gormleyalso O'Gormley, Grimley, Gormilly | Ó Goirmleaghaigh | descendant of Goirmshleaghach, 'blue-spearman' | Donegal, Tyrone, Derry / Londonderry |
| Grace | Grás | le gras — 'the stout' | Kilkenny, Laois |
| Greaneyalso Greany | Ó Gráinne | descendant of Gráinne — a woman's name | Kerry, Galway |
| Griffinalso O'Griffin, Griffey | Ó Gríobhtha | descendant of Gríobhtha, 'griffin-like' | Clare, Kerry, Limerick |
| Groganalso Groogan, Groggan | Ó Gruagáin | descendant of Gruagán — from gruag, hair, or grúg, fierceness | Roscommon |
| Guilfoylealso Gilfoyle, Kilfoyle, MacGilfoyle | Mac Giolla Phóil | son of the servant of St Paul | Offaly |
| Hackettalso Hacket | Haicéid | son of Haket, a Norman personal name | Dublin, Wicklow, Kilkenny, Tipperary |
| Halliganalso Hallagan, Hilligan, O'Halligan | Ó hAilleagáin | descendant of Ailleagán, a diminutive of áille, ‘handsome, beautiful’ | Mayo, Roscommon |
| Hallinanalso O'Hallinan, Halnan | Ó hAilgheanáin | descendant of Ailgheanán, 'noble offspring' | Cork, Limerick, Mayo |
| Halpinalso Halpenny, Halfpenny | Ó hAilpín | descendant of Ailpín | Monaghan, Limerick, Louth |
| Hamillalso Hammill, O'Hamill | Ó hÁdhmaill | descendant of Ádhmall, 'quick, ready, active' | Tyrone, Armagh |
| Hanafinalso Hanifin, Hanifan, Hanefan, O'Hanafin | Ó hAinbhtheáin | descendant of Ainbhtheán, a diminutive of Ainbhioth | Cork, Kerry |
| Hanleyalso Hanly, O'Hanley, Henly | Ó hÁinle | descendant of Áinle, 'beauty' or 'hero' | Roscommon |
| Hanlonalso O'Hanlon | Ó hAnluain | descendant of Anluan, 'great champion' | Armagh |
| Hanniganalso Hanigan | Ó hAnnagáin | descendant of Annagán — from annadh, delay | Limerick |
| Hannonalso Hannan, Hanan | Ó hAnnáin | descendant of Annán — from annadh, delay | Limerick |
| Hanrahanalso O'Hanrahan, Handrahan | Ó hAnradháin | descendant of Anradhán, 'warrior, champion' | Clare, Limerick, Tipperary |
| Hanrattyalso O'Hanratty | Ó hAnrachtaigh | descendant of Anrachtach, 'unlawful' | Monaghan, Armagh, Louth |
| Harkinalso Harkins, Harkan, Horkan, Horkin, O'Harkin | Ó hEarcáin | descendant of Earcán, a diminutive of earc, ‘red, speckled’ | Donegal, Derry / Londonderry, Mayo, Clare |
| Harnettalso Hartnett, Harnedy, O'Hartnedy, O'Harniady | Ó hAirtnéada | descendant of Airtnéada, 'battle-bear' or 'battle-stone' — a meaning Woulfe reconstructs rather than finds written | Limerick, Kerry, Cork |
| Harriganalso Horrigan, Herrigan | Ó hArragáin | descendant of Anradhán, 'warrior, champion' | Laois |
| Hartalso Harte, O'Hart, O'Harte | Ó hAirt | descendant of Art, ‘bear, stone, noble’ | Meath, Sligo |
| Hartiganalso O'Hartigan, Hartican | Ó hArtagáin | descendant of Artagán, 'little Art' | Clare, Limerick |
| Hassettalso Hassey | Ó hAiseadha | descendant of Aisidh, 'strife' | Clare, Limerick |
| Haydenalso Haydon, Haden, Headen, Heden, O'Hayden | Ó hEideáin | descendant of Eideadhán, a diminutive of Eideadh | Roscommon, Tipperary |
| Hayesalso O'Hea, Hughes (south) | Ó hAodha | descendant of Aodh, 'fire' | Cork, Limerick, Tipperary |
| Healyalso Healey, O'Healy | Ó hÉilidhe / Ó hÉalaighthe | 'claimant' (Sligo) or 'ingenious' (Cork) | Sligo, Cork |
| Heffernanalso Hiffernan, Hefferan, Heffernon, O'Heffernan | Ó hIfearnáin | descendant of Ifearnán | Limerick, Tipperary |
| Hegartyalso Hagarty, Hagerty, Heggerty | Ó hÁgartaigh | descendant of Fágartach | Donegal, Derry / Londonderry, Cork |
| Hehiralso O'Hehir, Hegher, Aher | Ó hAichir | descendant of Aichear, ‘sharp, bitter, angry’ | Clare, Limerick |
| Heneghanalso Henaghan, Heanaghan, Henehan, Henihan, O'Heneghan | Ó hÉineacháin | descendant of Eidhneachán | Mayo |
| Hennessyalso Hennessey | Ó hAonghusa | descendant of Aonghus | Cork, Offaly |
| Henryalso MacHenry, McHenry, Hendry, Henery, O'Henry | Ó hInneirghe | descendant of Inneirghe, ‘the rising, early riser’; or Mac Éinrí, son of Henry | Tyrone |
| Hessionalso Hessian, Hishon, Hussian | Ó hOisín | descendant of Oisín, a diminutive of os, ‘a deer’ | |
| Hickeyalso O'Hickey | Ó hÍcidhe | descendant of the healer (íce, 'healing') | Clare, Tipperary, Limerick |
| Higginsalso O'Higgins | Ó hUiginn | descendant of Uige, 'knowledge, skill' | Sligo, Mayo, Westmeath |
| Hoganalso O'Hogan | Ó hÓgáin | descendant of Ógán, 'the young one' | Tipperary, Clare |
| Horanalso Haran, Horahan | Ó hArracháin | descendant of Anradhán, 'warrior, champion' | Laois, Tipperary |
| Horealso Hoare | de Hór | hoar — 'grey-haired' | Wexford, Cork |
| Horganalso O'Horgan, Organ, Hargan | Ó hArgáin | descendant of Anradhán, 'warrior, champion' | Cork, Kerry |
| Hughesalso MacHugh, McHugh | Mac Aodha / Ó hAodha | son (or descendant) of Aodh, 'fire' | Armagh, Tyrone, Galway |
| Hurleyalso O'Hurley | Ó hUrthuile / Ó Muirthile | descendant of Urthuile — 'sea-tide' | Cork, Limerick, Clare |
| Hynesalso Heynes, Hyndes, O'Hynes | Ó hEidhin | descendant of Eidhean, ‘ivy’ | Galway, Clare, Limerick |
| Igoealso Igo, Iago | Mac Iagó | son of Iagó, a Spanish form of James | Roscommon |
| Jenkinsalso Jenkin, Jenkinson | — (Welsh / Cornish name) | 'little John' — Jenkin, a pet-form of John with the '-kin' ending | Antrim, Down, Limerick |
| Jenningsalso MacJonin, Jennynges | Mac Sheóinín | son of little John | Galway, Mayo |
| Johnstonalso Johnstone | Mac Seáin (sometimes) | John's town | Fermanagh, Down, Antrim |
| Joyce | Seoighe | from Josse, a Breton saint's name | Galway, Mayo |
| Kavanaghalso Cavanagh, Cavanaugh | Caomhánach | follower of St Caomhán | Carlow, Wexford |
| Kealyalso Keely, Quealy | Ó Caollaidhe | descendant of Caollaidhe | Kilkenny, Laois, Tipperary |
| Keanealso Kane, O'Cahan | Ó Catháin | descendant of Cathán, 'little battler' | Derry / Londonderry, Galway, Clare |
| Kearneyalso Carney | Ó Cearnaigh / Ó Catharnaigh | descendant of Cearnach, 'victorious' | Mayo, Tipperary, Meath |
| Kearnsalso Kerins, Kearn, Kerrin | Ó Céirín | descendant of Céirín — from ciar, black | Mayo |
| Keating | Céitinn | possibly Welsh cethin, 'dusky' | Tipperary, Wexford |
| Keaveneyalso Keaveny, MacKeaveney | Mac Géibheannaigh | son of Géibheannach, 'fettered' | Fermanagh, Sligo, Mayo |
| Keenanalso O'Keenan, Keenon | Ó Cianáin | descendant of Cianán, a diminutive of Cian, 'ancient' | Fermanagh |
| Kehoealso MacKehoe, Kehoe | Mac Eochaidh | son of Eochaidh — from each, 'horse' | Wexford, Wicklow |
| Kelleheralso Kelliher, Kellegher | Ó Céileachair | descendant of Céileachar, 'companion-loving' | Cork, Kerry |
| Kellyalso O'Kelly | Ó Ceallaigh | descendant of Ceallach, 'bright-headed' or 'strife' | Galway, Roscommon, Meath |
| Kennedyalso O'Kennedy | Ó Cinnéide | descendant of Cinnéidigh, 'helmeted head' | Tipperary, Clare |
| Kennyalso O'Kenny | Ó Cionnaith | descendant of Cionnaith | Galway, Roscommon |
| Keoghalso MacKeogh, Hoey | Mac Eochaidh | son of Eochaidh — from each, 'horse' | Roscommon, Tipperary, Wicklow |
| Kerriganalso Kergan, Comer | Ó Ciaragáin | descendant of Ciaragán — from ciar, black | Mayo, Donegal |
| Kielyalso Keeley, Queally | Ó Cadhla | descendant of Cadhla, 'graceful' | Waterford, Limerick |
| Kiernanalso MacKiernan, Kernan, Lord | Mac Tighearnáin | son of Tighearnán, 'little lord' | Cavan, Roscommon, Fermanagh |
| Kilcoynealso Kilcoyn, MacGillechyny | Mac Giolla Chaoine | son of the servant of St Caoine, or of 'the gentle youth' | Leitrim, Dublin |
| Killeenalso Killen, Killian, Killion, O'Killeen | Ó Cillín | descendant of Cillín, a pet form of Ceallach | Clare, Galway, Mayo, Westmeath, Offaly, Kildare, Down |
| Kinsellaalso Kinsela | Cinnsealach | of the Uí Cheinnsealaigh — the royal line of south Leinster | Wexford, Carlow, Wicklow |
| Kirbyalso O'Kirby | Ó Ciarmhaic | descendant of Ciarmhac, 'dark son' | Limerick, Kerry |
| Kirwanalso Kirwin, Quirevan | Ó Ciardubháin | descendant of Ciardhubhán, 'the black-dark one' | Galway |
| Kissanealso Cussane, O'Kissane | Ó Casáin | descendant of Casán — from cas, curly | Kerry, Galway |
| Laceyalso Lacy, De Lacy, de Lacy, Leacy | de Léis | Norman ‘de Laci’, of Lassy in France; or Ó Laitheasa, descendant of Flaitheas | Meath, Limerick, Wexford |
| Laloralso Lawlor, O'Lalor | Ó Leathlobhair | descendant of Leathlobhar | Laois, Kerry |
| Langanalso Longan, Langin, O'Langan, O'Longan | Ó Longáin | descendant of Longán, a diminutive of long, ‘tall’ | Armagh, Mayo, Limerick, Kerry, Cork |
| Larkinalso O'Larkin | Ó Lorcáin | descendant of Lorcán, 'fierce' | Galway, Armagh, Wexford |
| Lavertyalso Lafferty, O'Laverty | Ó Laithbheartaigh | descendant of Flaithbheartach | Tyrone, Derry / Londonderry, Antrim, Donegal |
| Lavinalso Lavan, Hand | Ó Láimhín | a corruption of Ó Flaithimhín | Roscommon, Mayo |
| Lawlessalso Lillis | Laighléis | Middle English ‘Laghles’, the outlaw | |
| Leahyalso O'Leahy, Leehy | Ó Laochdha | descendant of Laochdha, 'heroic' | Cork, Kerry, Limerick, Tipperary |
| Lehanealso Lyhane, O'Lehane | Ó Liatháin | descendant of Liathán, 'grey' | Cork, Sligo |
| Lenihanalso Lenehan, Lenaghan | Ó Léanacháin | descendant of Léanachán, 'mantled, cloaked' | Roscommon |
| Lennonalso O'Lennon, Leonard | Ó Leannáin | descendant of Leannán, 'lover' or 'sweetheart' | Fermanagh, Mayo, Galway |
| Linehanalso Linahan, Lunican | Ó Luingeacháin | descendant of Longachán | Cork, Limerick, Kerry |
| Loftusalso Loughnane | Ó Lachtnáin | descendant of Lachtnán, 'milk-white' | Mayo, Sligo |
| Lombard | Lombard | 'the Lombard' — an Italian banker | Cork |
| Lonerganalso Lonnergan, Londregan, Londrigan, Landregan, Lorrigan, O'Lonergan | Ó Longargáin | descendant of Longargán, a diminutive of lonngarg, ‘strong-fierce’ | Tipperary, Kilkenny, Waterford |
| Looneyalso Loonie | Ó Luanaigh | descendant of Luanach, 'warrior' (luan, champion) | Clare, Cork |
| Loughranalso O'Loughran, Lochrane, Loran | Ó Luchaireáin | descendant of Luchaireán, 'bright, glittering' | Armagh, Tyrone |
| Lowryalso Lowery, O'Lowry, Lowroo | Ó Labhradha | descendant of Labhraidh, ‘speaker, spokesman’ | Down |
| Luceyalso Lucy | Ó Luasaigh | a corruption of Mac Cluasaigh | Cork |
| Lunneyalso Lunny, Loney | Ó Luinigh | descendant of Luineach | Fermanagh, Tyrone |
| Lydonalso Leyden, Ludden, Lyden | Ó Lodáin | descendant of Lodán | Galway, Mayo, Clare |
| Lynamalso Lynham, Lyneham | Ó Laidhghneáin | descendant of Laidhghneán, 'snow-birth' | Wexford, Carlow |
| Lynchalso O'Lynch, Linchy | Ó Loingsigh / de Lench | descendant of Loingseach, 'mariner' | Galway, Cork, Clare |
| Lyonsalso Lyne, Lane, Leyne | Ó Laighin | descendant of Laighean, 'lance, spear' | Galway, Kildare, Kerry |
| Lysaghtalso MacLysaght, McLysaght, Lysat | Mac Giolla Iasachta | son of Giolla Iasachta, ‘strange youth’ | Clare |
| MacDermotalso McDermott, Dermott | Mac Diarmada | son of Diarmaid | Roscommon, Sligo |
| MacNamaraalso McNamara | Mac Conmara | son of Cú Mara, 'hound of the sea' | Clare |
| Maddenalso O'Madden | Ó Madáin | descendant of Madán (from madadh, 'hound') | Galway, Offaly |
| Madiganalso Maddigan | Ó Madagáin | the same as Ó Madáin (Madden) | Clare, Limerick |
| Mageealso McGee, MacGee | Mag Aoidh | son of Aodh, 'fire' | Antrim, Down, Donegal |
| Maguirealso McGuire, MacGuire | Mag Uidhir | son of Odhar, 'the dun-coloured' | Fermanagh |
| Maheralso Meagher, O'Meagher | Ó Meachair | descendant of Meachar, 'hospitable' | Tipperary |
| Malonealso O'Malone | Ó Maoileoin | descendant of Maoileoin, 'devotee of St John' | Offaly |
| Manganalso Mongan, Mangin, O'Mangan | Ó Mongáin | descendant of Mongán, a diminutive of mongach, ‘hairy’ | Cork, Mayo, Fermanagh |
| Mannionalso Manning, Manion, O'Mannin | Ó Mainnín | descendant of Mainnín — perhaps the same as Mainchín | Galway, Roscommon |
| Martinalso Martyn, Gilmartin | Mac Giolla Mháirtín / Máirtín | devotee of St Martin | Galway, Tyrone |
| Mastersonalso MacMaster, McMaster, Master | Mac an Mháighistir | son of the master, from máighistir (Latin magister) | Cavan, Longford, Roscommon, Wexford |
| McAleeralso MacAleer, MacLear, MacLure, McClure, MacClure | Mac Giolla Uidhir | son of Giolla Odhar, ‘the pale youth’ | Armagh |
| McAllisteralso MacAllister, MacAlister, McAlister, MacCallister, McCallister, MacAlester, McAlester, MacEllister, Callister | Mac Alastair | son of Alastar, a Gaelic form of Alexander | Antrim |
| McAndrewalso MacAndrew | Mac Aindriú | son of Andrew | Mayo |
| McArdlealso MacArdle, MacArdel, McCardle, MacCardle | Mac Árdghail | son of Árdghal, ‘high valour’ | |
| McBridealso MacBride, Kilbride | Mac Giolla Bhríde | son of the servant of St Brigid | Donegal |
| McCabealso MacCabe | Mac Cába | son of Cába | Cavan, Monaghan |
| McCaffreyalso MacCaffrey, Caffrey, Caffery, MacCaffery, McCaffery, MacGaffrey | Mac Gafraidh | son of Godfrey | Fermanagh |
| McCannalso MacCann, Canny | Mac Cana | son of Cana, 'wolf cub' — a young warrior | Armagh |
| McCarthyalso MacCarthy, Carthy | Mac Cárthaigh | son of Cárthach, 'loving' | Cork, Kerry |
| McConnellalso MacConnell, Connell | Mac Conaill | son of Conall — 'hound' and 'valour'; in Ulster also from Mac Dhòmhnaill | Antrim |
| McCormackalso McCormick, MacCormack | Mac Cormaic | son of Cormac, 'charioteer' | Longford, Roscommon, Dublin |
| McCulloughalso MacCullagh, McCulloch, Cullagh | Mac Cú Uladh | son of Cú Uladh, 'the Hound of Ulster' | Down |
| McDaidalso MacDaid, McDevitt, MacDevitt, Devitt, Davitt, MacDavitt, MacDavid | Mac Daibhéid | son of Davet, a diminutive of David | Donegal, Mayo |
| McDonaghalso MacDonagh, McDonough | Mac Donnchadha | son of Donnchadh | Sligo, Roscommon, Galway |
| McDonnellalso MacDonnell, McDonald | Mac Dónaill | son of Dónall | Antrim, Mayo |
| McElroyalso MacElroy, Gilroy, Kilroy | Mac Giolla Rua | son of the red-haired youth | Fermanagh |
| McEvoyalso MacEvoy, McAvoy, MacAvoy, MacVoy, Evoy | Mac Fhíodhbhuidhe | son of Fíodhbhadhach, ‘of the wood, woodman’ | Laois |
| McFaddenalso MacFadden, Patton, McFadyen | Mac Pháidín | son of Páidín, 'little Patrick' | Donegal, Mayo |
| McGaheyalso MacGahey, McGaughey, MacGaughey, McGahy, MacGahy, Gahey | Mag Eachaidh | son of Eochaidh, ‘rich in cattle’ | |
| McGalealso MacGale, McGail | Mac Cathail / Mac Cathmhaoil | son of Cathal, 'battle-mighty' — or of Cathmhaol, 'battle-chief'; the authorities differ | Tyrone |
| McGinleyalso MacGinley, Maginley, MacGinly, Ginley, Ginnelly | Mag Fhionnghaile | son of Fionnghal, ‘fair valour’ | Donegal, Westmeath, Longford |
| McGoldrickalso MacGoldrick, McGolrick, MacGolrick, Goldrick, Golrick, Magolrick | Mag Ualghairg | son of Ualgharg, ‘proud-fierce’ | Leitrim, Fermanagh, Donegal |
| McGoniglealso MacGonigle, McGonagle, MacGonagle, McGonigal, MacGonigal, Gunnigle | Mag Congail | a variant of Mac Congail; Woulfe gives no meaning here | Donegal |
| McGovernalso Magauran | Mág Shamhradháin | son of Samhradhán, 'summer's child' | Cavan, Leitrim |
| McGrathalso MacGrath, Magrath | Mac Craith | son of Mac Raith, 'son of grace' | Waterford, Fermanagh, Clare |
| McGuinnessalso Magennis, McGinnis | Mag Aonghusa | son of Aonghus | Down, Armagh |
| McInerneyalso MacInerney | Mac an Airchinnigh | son of the erenagh — the hereditary steward of church lands | Clare, Limerick |
| McIntyrealso MacIntyre, MacEntire, MacAntire, MacInteer, McAteer, MacAteer, Mateer, Minteer, MacTier | Mac an tSaoir | son of the craftsman, from saor, ‘a mason or carpenter’ | |
| McKennaalso MacKenna, Kenna | Mac Cionaoith | son of Cionaoth | Monaghan, Tyrone |
| McKeownalso MacKeown, Owens | Mac Eoin | son of Eoin or Eoghan — John, or the older Irish Eoghan | Antrim, Down |
| McLoughlinalso MacLoughlin, McLaughlin, O'Melaghlin, MacLachlan | Mac Lochlainn | son of Lochlann, 'the Norse-lander' | Donegal, Derry / Londonderry, Westmeath |
| McMahonalso MacMahon | Mac Mathghamhna | son of Mathghamhain, 'bear' | Clare, Monaghan |
| McManusalso MacManus, Manus | Mac Mághnais | son of Magnus — from Latin magnus, 'great' | Fermanagh, Roscommon |
| McNallyalso MacNally, Nally | Mac Con Allaidh | son of Cú Allaidh, 'the wild hound' — the wolf | Tyrone, Armagh, Monaghan |
| McNelisalso MacNelis, McNellis, Nelis | Mac Niallghuis | son of Niallghus, 'champion-choice' | Donegal |
| McNultyalso MacNulty, Nulty | Mac an Ultaigh | son of the Ulsterman | Donegal, Mayo |
| McVeighalso MacVeigh, McVey, MacVey, MacVeagh, McVeagh, MacVay | Mac an Bheatha | son of Mac an Bheathadh, a personal name meaning ‘son of life’ | |
| Meehanalso Meegan, O'Meehan | Ó Miadhacháin | descendant of Miadhachán, 'the honourable' | Leitrim, Fermanagh, Galway |
| Merriganalso Murrigan, Maragan, O'Merrigan | Ó Muireagáin | descendant of Muireagán, a diminutive of a name beginning Muir- | Westmeath, Longford, Down, Armagh |
| Minoguealso Minnogue, Minogue | Ó Muineog | descendant of Muineog — a diminutive of manach, 'monk' | Clare, Offaly |
| Mitchell | Mistéil | from Michael | Antrim, Down, Galway |
| Molloyalso O'Molloy, Mulloy | Ó Maolmhuaidh | descendant of Maolmhuadh, 'noble chief' | Offaly, Roscommon |
| Moloneyalso Molony, Mullowney | Ó Maoldhomhnaigh | descendant of Maoldomhnaigh, 'devoted to Sunday, or to the Church' | Clare, Limerick, Tipperary |
| Monaghanalso Monahan, Manahan, Monks | Ó Manacháin | descendant of Manachán, 'little monk' | Roscommon |
| Mooneyalso Moony, Meaney, Mainey | Ó Maonaigh | descendant of Maonach | Roscommon, Sligo, Galway |
| Moorealso O'More, O'Moore | Ó Mórdha | descendant of Mórdha, 'majestic' | Laois |
| Moranalso O'Moran, Morahan | Ó Móráin | descendant of Mórán, 'the great one' | Mayo, Roscommon, Leitrim |
| Moriartyalso O'Moriarty | Ó Muircheartaigh | descendant of Muircheartach, 'skilled navigator' — from muir, the sea | Kerry |
| Moroneyalso Mulrooney, Mulrony, Morooney, Murroney, O'Moroney | Ó Maolruanaidh | descendant of Maolruanaidh, ‘follower of Ruanaidh’ | Clare, Limerick, Tipperary, Fermanagh, Galway |
| Morrison | Mac Muiris / Ó Muirgheasáin | son of Maurice / descendant of Muirgheasán | Antrim, Down, Derry / Londonderry |
| Morrisseyalso Morrissy, Morissy, Morris | Ó Muirgheasa | descendant of Muirgheas, 'sea-choice' | Sligo |
| Moynihanalso Minihane, Minihan | Ó Muimhneacháin | descendant of the Munsterman | Kerry, Cork |
| Mulcahy | Ó Maolchathaigh | descendant of the devotee of St Cathach ('battle') | Tipperary, Waterford, Limerick |
| Muldoonalso Muldon, Meldon, O'Muldoon | Ó Maoldúin | descendant of Maoldúin, ‘chief of the fort’ | Fermanagh, Sligo |
| Mulgrewalso Mulcreevy, Mulgrave | Ó Maolchraoibhe | descendant of Maolchraoibhe, 'chief of Craobh' | Down, Tyrone, Armagh |
| Mulhallalso O'Mulhall | Ó Maolchathail | descendant of Maolchathail, ‘servant of St Cathal’ | Offaly, Laois |
| Mulhernalso Mulkern, Mulkerrin, Mulherron | Ó Maoilchiaráin | descendant of the servant of St Ciarán | Roscommon, Westmeath, Donegal |
| Mulhollandalso Mullholland, Mulholland | Ó Maolchalann | descendant of Maolchalann, 'chief of the calends' | Derry / Londonderry, Antrim |
| Mullallyalso Lally, O'Mullally | Ó Maolalaidh | descendant of Maolaladh, 'speckled chief' | Galway |
| Mullanalso Mullen, Mullins, MacMullan | Ó Maoláin | descendant of Maolán, 'the tonsured one' | Derry / Londonderry, Galway |
| Mullaneyalso Mullany, O'Mullany | Ó Maoileanaigh | descendant of Maolsheanaigh, ‘servant of St Seanach’ | Roscommon, Mayo, Sligo |
| Mullarkeyalso Malarky, Melarkey | Ó Maoilearca | descendant of the servant of St Earc | Donegal, Mayo, Sligo |
| Mulliganalso O'Mulligan | Ó Maolagáin | descendant of Maolagán, 'the little tonsured one' | Donegal, Mayo, Monaghan |
| Mulqueenalso Mulqueeny, Mulkeen | Ó Maolchaoin | descendant of Maolcaoin, 'gentle chief' | Clare, Limerick |
| Mulveyalso Mulvagh | Ó Maoilmhiadhaigh | descendant of Maolmiadhach, 'honourable chief' | Leitrim |
| Mulvihillalso O'Mulvihill, Melville | Ó Maoilmhichil | descendant of the servant of St Michael | Roscommon, Kerry, Limerick |
| Murphyalso O'Murphy, MacMurphy | Ó Murchadha | descendant of Murchadh, 'sea-warrior' | Wexford, Cork, Armagh |
| Murrayalso MacMurray, O'Murry | Ó Muireadhaigh / Mac Muireadhaigh | descendant of Muireadhach, 'seafarer / lord' | Roscommon, Down, Donegal |
| Murtaghalso Murtaugh, MacMurtry, Murdock | Mac Muircheartaigh | son of Muircheartach, 'sea-director, navigator' | Meath, Sligo |
| Naughtonalso O'Naughton, Norton, Nocton | Ó Neachtain | descendant of Neachtan — an old name linked to water | Galway, Clare, Roscommon |
| Nealonalso Neylon, Nilan, Niland | Ó Nialláin | descendant of Niallán, 'little Niall' | Clare, Galway |
| Nearyalso Nary | Ó Náradhaigh | descendant of Náradach, 'good, noble' | Mayo, Roscommon, Louth |
| Nevinalso MacNevin, Navin, Nevins | Mac Cnáimhín | son of Cnáimhín — from cnámh, bone | Galway |
| Nolanalso O'Nolan, Knowlan | Ó Nualláin | descendant of Nuallán, 'famous, noble' | Carlow, Wexford |
| Noonanalso Nunan | Ó Nuanáin | descendant of Ionmhaineán, 'the beloved' | Cork, Limerick |
| Normoylealso Normile | Mac Confhormaoile | son of Cú Fhormaoile, ‘hound of Formoyle’, a place in Co. Clare | Clare, Limerick |
| Nugent | Nuinseann | from Nogent in France | Westmeath, Cavan |
| O'Brienalso Brien, Bryan | Ó Briain | descendant of Brian (Boru) | Clare, Limerick, Tipperary |
| O'Callaghanalso Callaghan, Callahan | Ó Ceallacháin | descendant of Ceallachán of Cashel | Cork, Clare |
| O'Connellalso Connell, O'Connel | Ó Conaill | descendant of Conall — a name built from 'hound' and 'valour' | Kerry, Galway, Derry / Londonderry |
| O'Connoralso Connor, Connors, O'Conor | Ó Conchobhair | descendant of Conchobhar, 'lover of hounds' | Roscommon, Sligo, Kerry, Offaly |
| O'Deaalso Dea, Day, Dee | Ó Deághaidh | descendant of Deághaidh, a tenth-century chieftain | Clare |
| O'Donnellalso Donnell, O'Donel | Ó Domhnaill | descendant of Domhnall, 'world-ruler' | Donegal |
| O'Donoghuealso Donoghue, Donohoe, O'Donohue | Ó Donnchadha | descendant of Donnchadh | Kerry, Cork, Cavan |
| O'Dowdalso Dowd, Doody | Ó Dubhda | descendant of Dubhda, 'the dark' | Mayo, Sligo |
| O'Driscollalso Driscoll | Ó hEidirsceoil | descendant of the eidirsceol — 'the go-between, the interpreter' | Cork |
| O'Farrellalso Farrell, Ferrall | Ó Fearghail | descendant of Fearghal, 'man of valour' | Longford |
| O'Flahertyalso Flaherty | Ó Flaithbheartaigh | descendant of Flaithbheartach, 'bright ruler' | Galway, Mayo |
| O'Garaalso Gara, Geary, Guiry, O'Geary | Ó Gadhra | descendant of Gadhra, perhaps from gadhar, ‘a mastiff’ | Sligo, Mayo, Cork, Kerry, Limerick |
| O'Gradyalso Grady | Ó Gráda | descendant of Gráda, 'noble, illustrious' | Clare, Galway, Limerick |
| O'Haganalso Hagan, O'Hagen | Ó hAodhagáin | descendant of Aodhagán, a diminutive of Aodh, 'fire' | Tyrone, Armagh |
| O'Halloranalso Halloran | Ó hAllmhuráin | descendant of Allmhurán, 'the stranger from over the sea' | Clare, Galway |
| O'Haraalso Hara | Ó hEaghra | descendant of Eaghra of Luighne | Sligo, Antrim |
| O'Harealso Hare, Haire | Ó hÍr / Ó hAichir | descendant of Ír, 'long-lasting' — or of Aichear, 'fierce' | Armagh, Down, Louth |
| O'Keeffealso Keefe, Keeffe | Ó Caoimh | descendant of Caomh, 'gentle, beloved' | Cork |
| O'Learyalso Leary | Ó Laoghaire | descendant of Laoghaire, 'calf-keeper' | Cork |
| O'Mahonyalso Mahony, Mahon | Ó Mathghamhna | descendant of Mathghamhain, 'bear' | Cork, Kerry |
| O'Malleyalso Malley, Melia | Ó Máille | descendant of Máille — 'noble chief' | Mayo |
| O'Neillalso Neill, MacNeill | Ó Néill | descendant of Niall (Glúndub) | Tyrone, Antrim, Armagh |
| O'Rahillyalso Rahilly | Ó Raithile | descendant of Raithile | Kerry, Cork, Limerick |
| O'Reillyalso Reilly, Riley | Ó Raghallaigh | descendant of Raghallach | Cavan, Meath |
| O'Rourkealso Rourke, Rorke | Ó Ruairc | descendant of Ruarc (a Norse name) | Leitrim, Cavan |
| O'Shaughnessyalso Shaughnessy, O'Shannessy | Ó Seachnasaigh | descendant of Seachnasach | Galway, Limerick |
| O'Sheaalso Shea, Shee | Ó Séaghdha | descendant of Séaghdha, 'hawk-like, stately' | Kerry, Kilkenny |
| O'Sullivanalso Sullivan | Ó Súilleabháin | descendant of Súildubhán, 'dark-eyed one' | Cork, Kerry |
| O'Toolealso Toole | Ó Tuathail | descendant of Tuathal, 'ruler of the people' | Wicklow, Kildare |
| Pattersonalso Paterson, Pattison, Pattinson | Mac Páidín | son of Páidín, a pet form of Patrick | Galway, Mayo |
| Philbinalso MacPhilbin, Filbin | Mac Philbín | son of Philpin, a little Philip | Mayo |
| Plunkettalso Plunket | Pluincéid | Norman Blanchet, from French blanc, 'white, pale' | Meath, Louth, Dublin |
| Poweralso de Paor | de Paor | le poer — 'the poor man' (a crusader's vow) | Waterford |
| Prendergastalso Pender, Pendergast | de Priondargás | from Brontegeest in Flanders | Mayo, Tipperary, Wexford |
| Purcell | Puirséil | pourcel — 'piglet' (a herdsman's name) | Tipperary, Kilkenny |
| Quigleyalso O'Quigley, Quigg, Cogley | Ó Coigligh | descendant of Coigleach | Mayo, Sligo, Donegal |
| Quinlanalso Kinlan, Quinlivan, O'Quinlan | Ó Caoindealbháin | descendant of Caoindealbhán, 'gracefully shaped' | Meath, Tipperary, Kerry |
| Quinnalso O'Quinn | Ó Cuinn | descendant of Conn, 'chief' | Tyrone, Clare, Longford |
| Quirkealso Quirk, O'Quirke, Querk | Ó Cuirce | descendant of Corc, ‘heart’ | Tipperary, Cork, Kerry |
| Raffertyalso O'Rafferty, Raverty | Ó Raithbheartaigh | a corruption of Ó Robhartaigh | Tyrone, Donegal, Louth |
| Rafteryalso O'Raftery | Ó Reachtabhra | descendant of Reachtabhra — 'law' and 'fringe' | Mayo, Galway |
| Rattiganalso Ratigan, Rhatigan, Ratican, Raghtigan, Rhategan | Ó Reachtagáin | descendant of Reachtagán, a diminutive of reacht, ‘law, decree’ | Roscommon |
| Redmond | Réamonn | from Raymond (le Gros) | Wexford |
| Reganalso O'Regan, Reagan | Ó Riagáin | descendant of Riagán, 'little king' (or 'impulsive') | Laois, Cork, Meath |
| Reidyalso Ready, Readdy, O'Reidy | Ó Riada | descendant of Riada, ‘tamed, trained’ | Clare, Kerry |
| Reynoldsalso MacRannall, MacRandall | Mac Raghnaill | son of Raghnall — the Irish form of the Norse name Rögnvaldr | Leitrim |
| Ricealso Rhys | Rís | from Welsh Rhys | Kerry, Louth, Down |
| Rigneyalso O'Rigney | Ó Raigne | a variant of Ó Raighne; Woulfe gives no meaning here | Donegal, Offaly |
| Ringalso Reen, Rinn, Rynn, Wrynn | Ó Rinn | descendant of Reann, ‘spear’ | Cork, Roscommon |
| Riordanalso O'Riordan, Rearden | Ó Ríoghbhardáin | descendant of Ríoghbhardán, 'royal little bard' | Cork, Kerry |
| Rochealso de Roche | de Róiste | de la roche — 'of the rock' | Wexford, Cork, Limerick |
| Roddyalso Ruddy, Reddy, O'Roddy | Ó Rodaigh | descendant of Rodach, 'strong' | Galway, Leitrim |
| Roganalso O'Rogan | Ó Ruadhagáin | descendant of Ruadhagán — from ruadh, red | Armagh |
| Ronanalso Ronayne, O'Ronayne | Ó Rónáin | descendant of Rónán, 'little seal' | Cork, Longford, Mayo, Dublin |
| Rooneyalso O'Rooney | Ó Ruanaidh | descendant of Ruanadh, 'the champion' | Down, Fermanagh, Mayo |
| Ruanealso Rowan, Roane, Roan, Rouane, O'Ruane | Ó Ruadháin | descendant of Ruadhán, a diminutive of ruadh, ‘red’ | Mayo, Galway |
| Ryanalso O'Ryan, Mulryan | Ó Maoilriain | descendant of Maoilriaghain | Tipperary, Limerick |
| Savage | Sábhaois | le sauvage — 'the wild one' | Down |
| Scanlonalso Scanlan, O'Scanlon, Scannell | Ó Scannláin | descendant of Scannlán — from scannal, 'contention' or 'strife' | Cork, Kerry, Sligo |
| Scullyalso O'Scully | Ó Scolaidhe | descendant of the scholar | Tipperary, Westmeath |
| Seeryalso Seerey, O'Seery, Earner | Ó Saoraidhe | a later form of Ó Síoghradha, descendant of Síoghraidh, the Norse Sigefrith | Westmeath, Donegal, Mayo, Galway |
| Sextonalso Sexten, Shasnan | Ó Seasnáin | descendant of Seasnán | Limerick, Clare |
| Shanahanalso Shanaghan | Ó Seanacháin | descendant of Seanachán, 'the old, wise one' | Clare, Tipperary, Kerry |
| Shanleyalso MacShanley | Mac Seanlaoich | son of the old hero | Roscommon, Leitrim |
| Sharkeyalso O'Sharkey | Ó Searcaigh | descendant of Searcach, 'loving' | Tyrone, Donegal, Roscommon |
| Sheedyalso MacSheedy | Mac Síoda | son of Síoda, 'silk' | Clare, Limerick, Tipperary |
| Sheehanalso Sheahan | Ó Síodhacháin | descendant of Síodhach, 'the peaceful' | Limerick, Cork, Kerry |
| Sheehyalso MacSheehy | Mac Síthigh | son of Sítheach, 'the peaceful' — or 'the otherworldly' | Limerick, Kerry, Tipperary |
| Sheridanalso O'Sheridan | Ó Sirideáin | descendant of Sirideán, 'the seeker' | Cavan, Longford |
| Sherlock | Scurlóg | 'fair-locked' — bright-haired | Dublin, Meath, Kilkenny |
| Shielalso Shields, O'Shiel, Sheils | Ó Siadhail | descendant of Siadhal | Donegal, Westmeath, Offaly |
| Shinealso O'Shine | Ó Seighin | descendant of Seighin, 'wild ox' | Cork, Kerry, Limerick |
| Shortallalso Shortt | Seartal | 'short neck' (a nickname) | Kilkenny |
| Sinnottalso Synnott | Sionóid | sige-noth, 'victory-bold' | Wexford |
| Slattery | Ó Slatara | descendant of Slatra, 'the strong, bold' | Clare, Tipperary |
| Sloyanalso Sloyne, Sloan, Sloane | Ó Sluaghadháin | descendant of Sluaghadhán, a diminutive of Sluaghadhach, ‘belonging to a host’ | Mayo |
| Smithalso MacGowan, McGowan, Smyth | Mac Gabhann | son of the smith | Cavan, Leitrim |
| Spillanealso Spellane, Spelman, Smullen | Ó Spealáin | descendant of Spealán — from speal, a scythe | Tipperary, Sligo, Cork |
| Stack | Stac | uncertain — perhaps 'haystack-built' | Kerry |
| Stewartalso Stuart | Stíobhard | steward of the royal household | Antrim, Derry / Londonderry, Tyrone |
| Sugruealso Shughrue, Segrue | Ó Siocfhradha | descendant of Siocfhraidh — the Norse Sigefrith, 'victory-peace' | Kerry |
| Sweeneyalso MacSweeney, Sweeny | Mac Suibhne | son of Suibhne, 'well-going' | Donegal, Cork, Kerry |
| Taaffe | Táth | from Welsh Dafydd (David) | Louth, Sligo |
| Taggartalso MacTaggart, MacEntaggart, Teggart | Mac an tSagairt | son of the priest | Antrim, Down, Tyrone |
| Thompsonalso Thomson | Mac Thómais | son of Thomas | Antrim, Down |
| Tierneyalso O'Tierney | Ó Tighearnaigh | descendant of Tighearnach, 'lordly' | Mayo, Tipperary, Donegal |
| Tighealso Teague, Tague, Teige | Ó Taidhg | descendant of Tadhg, 'poet' | Roscommon, Mayo, Wicklow |
| Tobin | Tóibín | de St Aubyn | Tipperary, Kilkenny |
| Toneralso O'Toner | Ó Tomhrair | descendant of Tomhrar — a Norse personal name | Donegal, Armagh, Derry / Londonderry |
| Tormeyalso Tarmey | Ó Tormaigh | descendant of Thormodr — a common Norse personal name | Westmeath, Cavan |
| Traynoralso Treanor, MacCreanor, Trainor | Mac Thréinfhir | son of Tréanfhear, 'champion' — literally 'strong man' | Armagh, Monaghan, Tyrone |
| Treacyalso Tracy, Tracey | Ó Treasaigh | descendant of Treasach, 'the fierce, the warlike' | Galway, Laois, Tipperary |
| Troy | Ó Troighthigh | descendant of Troightheach, 'the foot-soldier' | Tipperary, Clare |
| Tullyalso MacTully, Flood | Mac an Tuile / Ó Maoltuile | son of the flood — 'of God's will' | Cavan, Longford, Galway |
| Tuohyalso Twohy, Toohy, Towey | Ó Tuathaigh | descendant of Tuathach, 'rustic' or 'lord' | Galway, Cork |
| Twomeyalso Toomey | Ó Tuama | descendant of Tuaim — 'burial mound' | Cork, Kerry |
| Tynanalso Tinan, Tivnan | Ó Teimhneáin | descendant of Teimhneán, 'dark, grey' | Laois, Kilkenny |
| Vaughan | Ó Mocháin / Vaughan | Welsh fychan, 'small' — adopted for Ó Mocháin | Clare, Mayo |
| Wall | de Bhál | du val — 'of the valley' | Limerick, Waterford, Carlow |
| Wallacealso Wallis | de Bhailís | le waleis — 'the Welshman, the foreigner' | Limerick, Waterford, Dublin |
| Walshalso Walshe, Brannagh, Breathnach | Breathnach | 'the Welshman' — soldiers who came with the Normans | Kilkenny, Mayo, Waterford |
| Wardalso MacWard | Mac an Bhaird | son of the bard | Donegal, Galway |
| Wattersalso Waters, MacWatters, Whoriskey, Toorish | Mac Uaitéir / Ó hUisce / Ó Fuaruisce | 'son of Walter' (Mac Uaitéir) — or, for the Gaelic septs, names built on 'uisce', water: 'descendant of the water' (Ó hUisce), 'cold water' (Ó Fuaruisce) | Louth, Donegal, Galway |
| Whelanalso Phelan, Whalen | Ó Faoláin | descendant of Faolán, 'little wolf' | Waterford, Kilkenny, Wexford |
| Woulfealso Wolfe | de Bhulbh | le woulf — 'the wolf' | Limerick, Kildare, Cork |
These arrived with the plantations and the Norman settlement and were never Gaelicised, so there is no older Irish version to give. Where a family adopted an Irish form later, it is shown on the name's own page.
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