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 |
| Ahern | Ó hEachthighearna | descendant of Eachthighearna, 'lord of horses' | Cork, Clare |
| Archer | Áirséir | the bowman | Kilkenny |
| Aylward | Aighleart | æthel-weard, 'noble guardian' | Waterford, Kilkenny |
| Barrett | Bairéid | possibly 'quarrelsome' (baraud) | Mayo, Cork |
| Barry | de Barra | from Barri in Wales | Cork |
| Beattie | Biadhtach (source) | from Bartholomew — or Irish biadhtach, 'public hospitaller' | Antrim, Fermanagh |
| Behan | Ó Beacháin | descendant of Beachán — from beach, 'bee' | Offaly, Laois |
| Bermingham | 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 |
| Boylan | Ó Baoighealláin | descendant of Baoigheallán | Monaghan |
| Boyle | Ó Baoighill | descendant of Baoigheall, 'vain pledge' | Donegal |
| Brady | Mac Brádaigh | son of Brádach, 'spirited' | Cavan |
| Brennan | Ó Braonáin | descendant of Braonán, 'little drop / sorrow' | Kilkenny, Roscommon, Sligo |
| Breslin | Ó Breisleáin | descendant of Breasal — the meaning of the personal name is not securely known | Donegal, Fermanagh |
| Brogan | Ó Brógáin | descendant of Brógán — probably from bróg, 'shoe' | Mayo, Donegal |
| Brophy | Ó Bróithe | descendant of Brothe | Laois, Kilkenny, Carlow |
| Brosnan | Ó Brosnacháin | of Brosna — the river and village in Kerry | Kerry |
| Buckley | Ó Buachalla | descendant of Buachaill, 'the herdsman' | Cork, Kerry |
| Burke | de Búrca | from de Burgh — 'of the borough' | Galway, Mayo |
| Butler | de Buitléir | le botiler — the (chief) butler of Ireland | Kilkenny, Tipperary |
| Byrne | Ó Broin | descendant of Bran, 'raven' | Wicklow, Dublin |
| Cagney | Ó Caingne | descendant of Caingne — from caingean, 'a legal dispute'; an advocate's name | Cork |
| Cahill | Ó Cathail | descendant of Cathal — cath, 'battle', with either 'rule' or 'great' | Galway, Kerry, Tipperary |
| Callan | Ó Cathaláin | descendant of Cathalán, 'little battle-mighty one' | Louth, Monaghan, Armagh |
| Campbell | Mac Cathmhaoil (adopted) | cam beul, 'crooked mouth' | Antrim, Down, Tyrone |
| Canavan | Ó Ceanndubháin | descendant of Ceanndubhán, 'the dark-headed one' | Galway, Cork |
| Cannon | Mac Canann | son of Cana, 'a whelp' or wolf cub | Donegal |
| Cantwell | Cantual | from Kentwell, Suffolk | Kilkenny, Tipperary |
| Carew | de Carrún | from Carew in Pembrokeshire — a place name, 'the fort by the ford' | Cork, Tipperary |
| Carey | Ó Ciardha / Ó Cearaigh | descendant of Ciardha, 'the dark one' — among several distinct roots | Kildare, Mayo, Cork |
| Carroll | Ó Cearbhaill | descendant of Cearbhall, 'fierce in battle' | Offaly, Tipperary, Louth |
| Carty | Ó Cárthaigh | descendant of Cárthach, 'loving' | Roscommon, Tipperary, Clare |
| Casey | Ó Cathasaigh | descendant of Cathasach, 'vigilant in war' | Cork, Dublin, Limerick |
| Cassidy | Ó Caiside | descendant of Caiside, 'curly-haired' | Fermanagh |
| Clancy | Mac Fhlannchaidh | son of Flannchadh, 'the red warrior' | Clare, Leitrim |
| Clarke | Ó Cléirigh | descendant of the cleric — possibly Europe's oldest surname (916 AD) | Donegal, Cavan, Galway |
| Cody | Mac Óda | son of Odo | Kilkenny, Wexford |
| Coffey | Ó Cobhthaigh | descendant of Cobhthach, 'victorious' | Westmeath, Longford, Cork |
| Coleman | Ó Colmáin / Ó Clumháin | descendant of Colmán, 'little dove' — from Latin columba | Sligo, Cork, Tipperary |
| Colgan | Ó Colgáin | descendant of Colga — from colg, 'sword' or 'thorn' | Offaly, Clare |
| Collins | Ó Coileáin | descendant of Coileán, 'young hound / whelp' | Cork, Limerick |
| Comerford | Comartún | from Comberford, Staffordshire | Kilkenny, Waterford |
| Comiskey | Mac Cumascaigh | son of Cumascach, 'the confuser' or 'mixer' | Monaghan, Cavan |
| Concannon | Ó Concheanainn | descendant of Cú Cheanainn, 'fair-headed hound' | Galway |
| Condon | Condún | de Caunteton — from Welsh Marches | Cork, Tipperary |
| Conlan | Ó Conalláin / Ó Caoindealbháin | descendant of Conallán — a diminutive of Conall | Roscommon, Tyrone, Meath |
| Conneely | Mac Conghaile / Ó Conghaile | son of Conghal — 'hound' and 'valour' | Galway, Mayo |
| Connery | Ó Conaire | descendant of Conaire, 'keeper of the hound' | Waterford, Wexford |
| Connolly | Ó Conghalaigh | descendant of Conghalach, 'valiant as a hound' | Monaghan, Galway, Meath |
| Considine | Mac Consaidín | son of Constantine | Clare |
| Coogan | Mac Cogadháin | son of Cogadhán — from cogadh, 'war' | Kilkenny |
| Cooney | Ó Cuana | descendant of Cuana | Tyrone, Galway, Clare |
| Corcoran | Ó Corcráin | descendant of Corcrán, 'purple-faced' | Tipperary, Offaly, Fermanagh |
| Corrigan | Ó Corragáin | descendant of Corragán | Fermanagh, Monaghan |
| Costello | Mac Oisdealbhaigh | son of Oisdealbh — the first Norman family to take a 'Mac' | Mayo, Galway |
| Coughlan | Ó Cochláin / Mac Cochláin | descendant or son of Cochlán — from cochall, 'cloak' or 'hood' | Cork, Offaly |
| Coyne | Ó Cadhain | descendant of Cadhan — a personal name from the barnacle goose | Galway, Mayo |
| Creagh | Craobhach | 'of the branch' — from craobh, a branch | Clare, Limerick |
| Cronin | Ó Cróinín | descendant of Crónín, 'little dark-yellow one' | Cork, Kerry |
| Crowley | Ó Cruadhlaoich | descendant of Cruadhlaoch, 'hard hero' | Cork |
| Cullen | Ó Cuilinn | descendant of Cuileann, 'holly' | Wicklow, Wexford, Kildare |
| Culloty | Ó Codlata | descendant of Codladh, 'sleep' | Kerry, Cork |
| Curran | Ó Corráin | descendant of Corrán | Donegal, Waterford, Kerry, Leitrim |
| Cusack | Ciomhsóg | from Cussac in Guyenne | Meath, Clare |
| Daly | Ó Dálaigh | descendant of Dálach, 'of the assembly' | Westmeath, Cork, Galway |
| Darcy | Ó Dorchaidhe / d'Arcy | descendant of Dorchaidh, 'dark one' — or from Arcy in France | Galway, Meath, Wexford |
| Deasy | Déiseach | 'of the Déise' — a man of the Déise people | Waterford, Cork |
| Delaney | Ó Dubhshláine | descendant of Dubhshláine, 'dark one of the Slaney' | Laois, Kilkenny |
| Dempsey | Ó Díomasaigh | descendant of Díomasach, 'the proud' | Laois, Offaly |
| Dennehy | Ó Duineachdha | descendant of Duineachaidh — read as 'humane' | Cork |
| Desmond | Deasmhumhnach | 'the south-Munster man' | Cork |
| Devaney | Ó Duibheamhna | descendant of Dubheamhain — dubh, 'black', with Eamhain, the old name of Navan Fort | Armagh, Down |
| Devereux | Deabhrús | from Évreux in Normandy | Wexford |
| Devine | Ó Daimhín | descendant of Daimhín | Fermanagh |
| Devlin | Ó Doibhilin | descendant of Doibhilean | Tyrone, Derry / Londonderry |
| Díaz | — (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 |
| Dinneen | Ó Duinnín | descendant of Duinnín, a diminutive of donn, 'brown' | Cork |
| Doherty | Ó Dochartaigh | descendant of Dochartach, 'the hurtful' | Donegal, Derry / Londonderry |
| Dolan | Ó Dobhailen | descendant of Dobhailen | Roscommon, Galway, Cavan |
| Donegan | Ó Donnagáin | descendant of Donnagán — a diminutive of donn, 'the dark one' or 'brown' | Cork, Tipperary, Monaghan |
| Donnellan | Ó Domhnalláin | descendant of Domhnallán, a diminutive of Domhnall, 'world-ruler' | Galway, Roscommon |
| Donnelly | Ó Donnghaile | descendant of Donnghal, 'brown valour' | Tyrone |
| Donovan | Ó Donnabháin | descendant of Donndubhán, 'dark brown-haired chief' | Cork, Limerick |
| Dooley | Ó Dubhlaoich | descendant of Dubhlaoch — dubh, 'dark', and laoch, 'warrior' | Offaly, Laois |
| Doran | Ó Deoráin | descendant of Deoradhán, 'the exile, the pilgrim' | Wexford, Laois, Down |
| Dowling | Ó Dúnlaing | descendant of Dúnlang | Laois, Cork, Kerry |
| Downey | Ó Duibheanaigh / Ó Maoldomhnaigh | descendant of Duibheanach — or, for the second sept, 'devotee of the church' | Galway, Cork, Kerry |
| Doyle | Ó Dubhghaill | descendant of Dubhghall, 'dark foreigner' — a Viking | Wexford, Wicklow, Dublin |
| Duff | Ó Duibh | descendant of Dubh, 'the black' or 'dark' | Laois |
| Duffy | Ó Dubhthaigh | descendant of Dubhthach, 'the dark one' | Monaghan, Donegal, Roscommon |
| Duggan | Ó Dubhagáin | descendant of Dubhagán, 'the little dark one' | Cork, Galway |
| Dunne | Ó Doinn | descendant of Donn, 'the brown-haired' (or the god of the dead) | Laois |
| Egan | Mac Aodhagáin | son of little Aodh | Galway, Tipperary, Offaly |
| Esmonde | Easmonn | east-mund, 'grace-protector' | Wexford |
| Fahy | Ó Fathaigh | descendant of Fathadh, 'foundation / green field' | Galway |
| Fallon | Ó Fallamhain | descendant of Fallamhan, 'leader' | Roscommon, Galway |
| Farley | Ó Faircheallaigh | descendant of Faircheallach | Cavan |
| Ferguson | Mac Fearghusa | son of Fearghus, 'man-strength' | Antrim, Down |
| Finnegan | Ó Fionnagáin | descendant of Fionnagán, 'little fair one' | Cavan, Monaghan, Galway |
| Fitzgerald | Mac Gearailt | fitz Gerald — son of Gerald (of Windsor) | Kildare, Kerry, Limerick |
| Fitzgibbon | 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 |
| Fitzsimons | Mac Síomóin | son of Simon | Meath, Cavan, Dublin |
| Flanagan | Ó Flannagáin | descendant of Flannagán, 'little red one' | Roscommon, Fermanagh, Offaly |
| Fleming | Pléimeann | 'the Fleming' — from Flanders | Meath, Louth |
| Flynn | Ó Floinn | descendant of Flann, 'ruddy' | Cork, Roscommon, Antrim |
| Fogarty | Ó Fógartaigh | descendant of Fógartach, 'the banished' or 'proclaimed' | Tipperary |
| Foley | Ó Foghladha | descendant of Foghlaidh — 'the plunderer' | Waterford, Kerry, Cork |
| Forde | 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 |
| French | de Fréins | 'the Frenchman' | Galway, Roscommon, Wexford |
| Furlong | Furlong | from the furrow-length of a ploughed field | Wexford |
| Gallagher | Ó Gallchobhair | descendant of Gallchobhar, 'foreign help' | Donegal |
| Galvin | Ó Gealbháin | descendant of Gealbhán, 'bright-white' | Kerry, Clare, Cork |
| Garvey | Ó Gairbhith | descendant of Gairbhith, 'rough peace' | Armagh, Down, Mayo |
| Geoghegan | Mag Eochagáin | son of Eochagán, from Eochaidh — a name built on each, 'horse' | Westmeath |
| Gill | Mac an Ghoill | son of the foreigner | Mayo, Donegal, Down |
| Gorman | Mac Gormáin | son of Gormán, 'the noble dark one' | Laois, Clare, Monaghan |
| Grace | Grás | le gras — 'the stout' | Kilkenny, Laois |
| Griffin | Ó Gríobhtha | descendant of Gríobhtha, 'griffin-like' | Clare, Kerry, Limerick |
| Halpin | Ó hAilpín | descendant of Ailpín | Monaghan, Limerick, Louth |
| Hanlon | Ó hAnluain | descendant of Anluan, 'great champion' | Armagh |
| Hayes | Ó hAodha | descendant of Aodh, 'fire' | Cork, Limerick, Tipperary |
| Healy | Ó hÉilidhe / Ó hÉalaighthe | 'claimant' (Sligo) or 'ingenious' (Cork) | Sligo, Cork |
| Hennessy | Ó hAonghusa | descendant of Aonghus | Cork, Offaly |
| Hickey | Ó hÍcidhe | descendant of the healer (íce, 'healing') | Clare, Tipperary, Limerick |
| Higgins | Ó hUiginn | descendant of Uiginn — 'the Viking' | Sligo, Mayo, Westmeath |
| Hogan | Ó hÓgáin | descendant of Ógán, 'the young one' | Tipperary, Clare |
| Hore | de Hór | hoar — 'grey-haired' | Wexford, Cork |
| Hughes | Mac Aodha / Ó hAodha | son (or descendant) of Aodh, 'fire' | Armagh, Tyrone, Galway |
| Hurley | Ó hUrthuile / Ó Muirthile | descendant of Urthuile — 'sea-tide' | Cork, Limerick, Clare |
| Jenkins | — (Welsh / Cornish name) | 'little John' — Jenkin, a pet-form of John with the '-kin' ending | Antrim, Down, Limerick |
| Jennings | Mac Sheóinín | son of little John | Galway, Mayo |
| Johnston | Mac Seáin (sometimes) | John's town | Fermanagh, Down, Antrim |
| Joyce | Seoighe | from Josse, a Breton saint's name | Galway, Mayo |
| Kavanagh | Caomhánach | follower of St Caomhán | Carlow, Wexford |
| Keane | Ó Catháin | descendant of Cathán, 'little battler' | Derry / Londonderry, Galway, Clare |
| Kearney | Ó Cearnaigh / Ó Catharnaigh | descendant of Cearnach, 'victorious' | Mayo, Tipperary, Meath |
| Keating | Céitinn | possibly Welsh cethin, 'dusky' | Tipperary, Wexford |
| Keenan | Ó Cianáin | descendant of Cianán, a diminutive of Cian, 'ancient' | Fermanagh |
| Kehoe | Mac Eochaidh | son of Eochaidh — from each, 'horse' | Wexford, Wicklow |
| Kelleher | Ó Céileachair | descendant of Céileachar, 'companion-loving' | Cork, Kerry |
| Kelly | Ó Ceallaigh | descendant of Ceallach, 'bright-headed' or 'strife' | Galway, Roscommon, Meath |
| Kennedy | Ó Cinnéide | descendant of Cinnéidigh, 'helmeted head' | Tipperary, Clare |
| Kenny | Ó Cionnaith | descendant of Cionnaith | Galway, Roscommon |
| Keogh | Mac Eochaidh | son of Eochaidh — from each, 'horse' | Roscommon, Tipperary, Wicklow |
| Kiely | Ó Cadhla | descendant of Cadhla, 'graceful' | Waterford, Limerick |
| Kinsella | Cinnsealach | of the Uí Cheinnsealaigh — the royal line of south Leinster | Wexford, Carlow, Wicklow |
| Kirby | Ó Ciarmhaic | descendant of Ciarmhac, 'dark son' | Limerick, Kerry |
| Kirwan | Ó Ciardhubháin | descendant of Ciardhubhán, 'the black-dark one' | Galway |
| Lalor | Ó Leathlobhair | descendant of Leathlobhar | Laois, Kerry |
| Larkin | Ó Lorcáin | descendant of Lorcán, 'fierce' | Galway, Armagh, Wexford |
| Lennon | Ó Leannáin | descendant of Leannán, 'lover' or 'sweetheart' | Fermanagh, Mayo, Galway |
| Loftus | Ó Lachtnáin | descendant of Lachtnán, 'milk-white' | Mayo, Sligo |
| Lombard | Lombard | 'the Lombard' — an Italian banker | Cork |
| Looney | Ó Luanaigh | descendant of Luanach, 'warrior' (luan, champion) | Clare, Cork |
| Lynch | Ó Loingsigh / de Lench | descendant of Loingseach, 'mariner' | Galway, Cork, Clare |
| MacDermot | Mac Diarmada | son of Diarmaid | Roscommon, Sligo |
| MacNamara | Mac Conmara | son of Cú Mara, 'hound of the sea' | Clare |
| Madden | Ó Madáin | descendant of Madán (from madadh, 'hound') | Galway, Offaly |
| Magee | Mag Aoidh | son of Aodh, 'fire' | Antrim, Down, Donegal |
| Maguire | Mag Uidhir | son of Odhar, 'the dun-coloured' | Fermanagh |
| Maher | Ó Meachair | descendant of Meachar, 'hospitable' | Tipperary |
| Malone | Ó Maoileoin | descendant of Maoileoin, 'devotee of St John' | Offaly |
| Martin | Mac Giolla Mháirtín / Máirtín | devotee of St Martin | Galway, Tyrone |
| McBride | Mac Giolla Bhríde | son of the servant of St Brigid | Donegal |
| McCabe | Mac Cába | son of Cába | Cavan, Monaghan |
| McCann | Mac Cana | son of Cana, 'wolf cub' — a young warrior | Armagh |
| McCarthy | Mac Cárthaigh | son of Cárthach, 'loving' | Cork, Kerry |
| McConnell | Mac Conaill | son of Conall — 'hound' and 'valour'; in Ulster also from Mac Dhòmhnaill | Antrim |
| McCormack | Mac Cormaic | son of Cormac, 'charioteer' | Longford, Roscommon, Dublin |
| McCullough | Mac Cú Uladh | son of Cú Uladh, 'the Hound of Ulster' | Down |
| McDonagh | Mac Donnchadha | son of Donnchadh | Sligo, Roscommon, Galway |
| McDonnell | Mac Dónaill | son of Dónall | Antrim, Mayo |
| McElroy | Mac Giolla Rua | son of the red-haired youth | Fermanagh |
| McFadden | Mac Pháidín | son of Páidín, 'little Patrick' | Donegal, Mayo |
| McGale | Mac Cathail / Mac Cathmhaoil | son of Cathal, 'battle-mighty' — or of Cathmhaol, 'battle-chief'; the authorities differ | Tyrone |
| McGovern | Mág Shamhradháin | son of Samhradhán, 'summer's child' | Cavan, Leitrim |
| McGrath | Mac Craith | son of Mac Raith, 'son of grace' | Waterford, Fermanagh, Clare |
| McGuinness | Mag Aonghusa | son of Aonghus | Down, Armagh |
| McInerney | Mac an Airchinnigh | son of the erenagh — the hereditary steward of church lands | Clare, Limerick |
| McKenna | Mac Cionaoith | son of Cionaoth | Monaghan, Tyrone |
| McKeown | Mac Eoin | son of Eoin or Eoghan — John, or the older Irish Eoghan | Antrim, Down |
| McLoughlin | Mac Lochlainn | son of Lochlann, 'the Norse-lander' | Donegal, Derry / Londonderry, Westmeath |
| McMahon | Mac Mathghamhna | son of Mathghamhain, 'bear' | Clare, Monaghan |
| McManus | Mac Mághnais | son of Magnus — from Latin magnus, 'great' | Fermanagh, Roscommon |
| McNally | Mac Con Allaidh | son of Cú Allaidh, 'the wild hound' — the wolf | Tyrone, Armagh, Monaghan |
| McNelis | Mac Niallais | son of Niallas, a name formed on Niall, 'champion' | Donegal |
| McNulty | Mac an Ultaigh | son of the Ulsterman | Donegal, Mayo |
| Meehan | Ó Miadhacháin | descendant of Miadhachán, 'the honourable' | Leitrim, Fermanagh, Galway |
| Minogue | Ó Muineog | descendant of Muineog — a diminutive of manach, 'monk' | Clare, Offaly |
| Mitchell | Mistéil | from Michael | Antrim, Down, Galway |
| Molloy | Ó Maolmhuaidh | descendant of Maolmhuadh, 'noble chief' | Offaly, Roscommon |
| Mooney | Ó Maonaigh | descendant of Maonach | Roscommon, Sligo, Galway |
| Moore | Ó Mórdha | descendant of Mórdha, 'majestic' | Laois |
| Moran | Ó Móráin | descendant of Mórán, 'the great one' | Mayo, Roscommon, Leitrim |
| Moriarty | Ó Muircheartaigh | descendant of Muircheartach, 'skilled navigator' — from muir, the sea | Kerry |
| Morrison | Mac Muiris / Ó Muirgheasáin | son of Maurice / descendant of Muirgheasán | Antrim, Down, Derry / Londonderry |
| Moynihan | Ó Muimhneacháin | descendant of the Munsterman | Kerry, Cork |
| Mulcahy | Ó Maolchathaigh | descendant of the devotee of St Cathach ('battle') | Tipperary, Waterford, Limerick |
| Mulholland | Ó Maolchalann | descendant of Maolchalann, 'chief of the calends' | Derry / Londonderry, Antrim |
| Mullan | Ó Maoláin | descendant of Maolán, 'the tonsured one' | Derry / Londonderry, Galway |
| Mulligan | Ó Maolagáin | descendant of Maolagán, 'the little tonsured one' | Donegal, Mayo, Monaghan |
| Murphy | Ó Murchadha | descendant of Murchadh, 'sea-warrior' | Wexford, Cork, Armagh |
| Murray | Ó Muireadhaigh / Mac Muireadhaigh | descendant of Muireadhach, 'seafarer / lord' | Roscommon, Down, Donegal |
| Naughton | Ó Neachtain | descendant of Neachtan — an old name linked to water | Galway, Clare, Roscommon |
| Nolan | Ó Nualláin | descendant of Nuallán, 'famous, noble' | Carlow, Wexford |
| Noonan | Ó Nuanáin | descendant of Ionmhaineán, 'the beloved' | Cork, Limerick |
| Nugent | Nuinseann | from Nogent in France | Westmeath, Cavan |
| O'Brien | Ó Briain | descendant of Brian (Boru) | Clare, Limerick, Tipperary |
| O'Callaghan | Ó Ceallacháin | descendant of Ceallachán of Cashel | Cork, Clare |
| O'Connell | Ó Conaill | descendant of Conall — a name built from 'hound' and 'valour' | Kerry, Galway, Derry / Londonderry |
| O'Connor | Ó Conchobhair | descendant of Conchobhar, 'lover of hounds' | Roscommon, Sligo, Kerry, Offaly |
| O'Dea | Ó Deághaidh | descendant of Deághaidh, a tenth-century chieftain | Clare |
| O'Donnell | Ó Domhnaill | descendant of Domhnall, 'world-ruler' | Donegal |
| O'Donoghue | Ó Donnchadha | descendant of Donnchadh | Kerry, Cork, Cavan |
| O'Dowd | Ó Dubhda | descendant of Dubhda, 'the dark' | Mayo, Sligo |
| O'Driscoll | Ó hEidirsceoil | descendant of the eidirsceol — 'the go-between, the interpreter' | Cork |
| O'Farrell | Ó Fearghail | descendant of Fearghal, 'man of valour' | Longford |
| O'Flaherty | Ó Flaithbheartaigh | descendant of Flaithbheartach, 'bright ruler' | Galway, Mayo |
| O'Hagan | Ó hAodhagáin | descendant of Aodhagán, a diminutive of Aodh, 'fire' | Tyrone, Armagh |
| O'Halloran | Ó hAllmhuráin | descendant of Allmhurán, 'the stranger from over the sea' | Clare, Galway |
| O'Hara | Ó hEaghra | descendant of Eaghra of Luighne | Sligo, Antrim |
| O'Hare | Ó hÍr / Ó hAichir | descendant of Ír, 'long-lasting' — or of Aichear, 'fierce' | Armagh, Down, Louth |
| O'Keeffe | Ó Caoimh | descendant of Caomh, 'gentle, beloved' | Cork |
| O'Leary | Ó Laoghaire | descendant of Laoghaire, 'calf-keeper' | Cork |
| O'Mahony | Ó Mathghamhna | descendant of Mathghamhain, 'bear' | Cork, Kerry |
| O'Malley | Ó Máille | descendant of Máille — 'noble chief' | Mayo |
| O'Neill | Ó Néill | descendant of Niall (Glúndub) | Tyrone, Antrim, Armagh |
| O'Reilly | Ó Raghallaigh | descendant of Raghallach | Cavan, Meath |
| O'Rourke | Ó Ruairc | descendant of Ruarc (a Norse name) | Leitrim, Cavan |
| O'Shea | Ó Séaghdha | descendant of Séaghdha, 'hawk-like, stately' | Kerry, Kilkenny |
| O'Sullivan | Ó Súilleabháin | descendant of Súildubhán, 'dark-eyed one' | Cork, Kerry |
| O'Toole | Ó Tuathail | descendant of Tuathal, 'ruler of the people' | Wicklow, Kildare |
| Plunkett | Pluincéid | possibly from blanchet, 'little fair one' | Meath, Louth, Dublin |
| Power | de Paor | le poer — 'the poor man' (a crusader's vow) | Waterford |
| Prendergast | de Priondargás | from Brontegeest in Flanders | Mayo, Tipperary, Wexford |
| Purcell | Puirséil | pourcel — 'piglet' (a herdsman's name) | Tipperary, Kilkenny |
| Quigley | Ó Coigligh | descendant of Coigleach | Mayo, Sligo, Donegal |
| Quinn | Ó Cuinn | descendant of Conn, 'chief' | Tyrone, Clare, Longford |
| Redmond | Réamonn | from Raymond (le Gros) | Wexford |
| Regan | Ó Riagáin | descendant of Riagán, 'little king' (or 'impulsive') | Laois, Cork, Meath |
| Reynolds | Mac Raghnaill | son of Raghnall — the Irish form of the Norse name Rögnvaldr | Leitrim |
| Rice | Rís | from Welsh Rhys | Kerry, Louth, Down |
| Riordan | Ó Ríoghbhardáin | descendant of Ríoghbhardán, 'royal little bard' | Cork, Kerry |
| Roche | de Róiste | de la roche — 'of the rock' | Wexford, Cork, Limerick |
| Rooney | Ó Ruanaidh | descendant of Ruanadh, 'the champion' | Down, Fermanagh, Mayo |
| Ryan | Ó Maoilriain | descendant of Maoilriaghain | Tipperary, Limerick |
| Savage | Sábhaois | le sauvage — 'the wild one' | Down |
| Scanlon | Ó Scannláin | descendant of Scannlán — from scannal, 'contention' or 'strife' | Cork, Kerry, Sligo |
| Scully | Ó Scolaidhe | descendant of the scholar | Tipperary, Westmeath |
| Shanahan | Ó Seanacháin | descendant of Seanachán, 'the old, wise one' | Clare, Tipperary, Kerry |
| Sheehan | Ó Síodhacháin | descendant of Síodhach, 'the peaceful' | Limerick, Cork, Kerry |
| Sheehy | Mac Síthigh | son of Sítheach, 'the peaceful' — or 'the otherworldly' | Limerick, Kerry, Tipperary |
| Sheridan | Ó Sirideáin | descendant of Sirideán, 'the seeker' | Cavan, Longford |
| Sherlock | Scurlóg | 'fair-locked' — bright-haired | Dublin, Meath, Kilkenny |
| Shortall | Seartal | 'short neck' (a nickname) | Kilkenny |
| Sinnott | Sionóid | sige-noth, 'victory-bold' | Wexford |
| Slattery | Ó Slatara | descendant of Slatra, 'the strong, bold' | Clare, Tipperary |
| Smith | Mac Gabhann | son of the smith | Cavan, Leitrim |
| Stack | Stac | uncertain — perhaps 'haystack-built' | Kerry |
| Sweeney | Mac Suibhne | son of Suibhne, 'well-going' | Donegal, Cork, Kerry |
| Taaffe | Táth | from Welsh Dafydd (David) | Louth, Sligo |
| Thompson | Mac Thómais | son of Thomas | Antrim, Down |
| Tierney | Ó Tighearnaigh | descendant of Tighearnach, 'lordly' | Mayo, Tipperary, Donegal |
| Tobin | Tóibín | de St Aubyn | Tipperary, Kilkenny |
| Treacy | Ó Treasaigh | descendant of Treasach, 'the fierce, the warlike' | Galway, Laois, Tipperary |
| Troy | Ó Troighthigh | descendant of Troightheach, 'the foot-soldier' | Tipperary, Clare |
| Tully | Mac an Tuile / Ó Maoltuile | son of the flood — 'of God's will' | Cavan, Longford, Galway |
| Twomey | Ó Tuama | descendant of Tuaim — 'burial mound' | Cork, Kerry |
| Vaughan | Ó Mocháin / Vaughan | Welsh fychan, 'small' — adopted for Ó Mocháin | Clare, Mayo |
| Wall | de Bhál | du val — 'of the valley' | Limerick, Waterford, Carlow |
| Wallace | de Bhailís | le waleis — 'the Welshman, the foreigner' | Limerick, Waterford, Dublin |
| Walsh | Breathnach | 'the Welshman' — soldiers who came with the Normans | Kilkenny, Mayo, Waterford |
| Ward | Mac an Bhaird | son of the bard | Donegal, Galway |
| Watters | 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 |
| Whelan | Ó Faoláin | descendant of Faolán, 'little wolf' | Waterford, Kilkenny, Wexford |
| Woulfe | 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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