Twenty names carried by a remarkable share of the island. Every one of them began as a claim of descent from a single named man — and most of them belong to several unrelated families who happen to share an ancestor's first name.
| # | Surname | In Irish | What it means | Homeland |
|---|---|---|---|---|
| 1 | Murphy | Ó Murchadha | descendant of Murchadh, 'sea-warrior' | Wexford, Cork, Armagh |
| 2 | Kelly | Ó Ceallaigh | descendant of Ceallach, 'bright-headed' or 'strife' | Galway, Roscommon, Meath |
| 3 | O'Sullivan | Ó Súilleabháin | descendant of Súildubhán, 'dark-eyed one' | Cork, Kerry |
| 4 | Walsh | Breathnach | 'the Welshman' — soldiers who came with the Normans | Kilkenny, Mayo, Waterford |
| 5 | Smith | Mac Gabhann | son of the smith | Cavan, Leitrim |
| 6 | O'Brien | Ó Briain | descendant of Brian (Boru) | Clare, Limerick, Tipperary |
| 7 | Byrne | Ó Broin | descendant of Bran, 'raven' | Wicklow, Dublin |
| 8 | Ryan | Ó Maoilriain | descendant of Maoilriaghain | Tipperary, Limerick |
| 9 | O'Connor | Ó Conchobhair | descendant of Conchobhar, 'lover of hounds' | Roscommon, Sligo, Kerry, Offaly |
| 10 | O'Neill | Ó Néill | descendant of Niall (Glúndub) | Tyrone, Antrim, Armagh |
| 11 | O'Reilly | Ó Raghallaigh | descendant of Raghallach | Cavan, Meath |
| 12 | Doyle | Ó Dubhghaill | descendant of Dubhghall, 'dark foreigner' — a Viking | Wexford, Wicklow, Dublin |
| 13 | McCarthy | Mac Cárthaigh | son of Cárthach, 'loving' | Cork, Kerry |
| 14 | Gallagher | Ó Gallchobhair | descendant of Gallchobhar, 'foreign help' | Donegal |
| 15 | Doherty | Ó Dochartaigh | descendant of Dochartach, 'the hurtful' | Donegal, Derry / Londonderry |
| 16 | Kennedy | Ó Cinnéide | descendant of Cinnéidigh, 'helmeted head' | Tipperary, Clare |
| 17 | Lynch | Ó Loingsigh / de Lench | descendant of Loingseach, 'mariner' | Galway, Cork, Clare |
| 18 | Murray | Ó Muireadhaigh / Mac Muireadhaigh | descendant of Muireadhach, 'seafarer / lord' | Roscommon, Down, Donegal |
| 19 | Quinn | Ó Cuinn | descendant of Conn, 'chief' | Tyrone, Clare, Longford |
| 20 | Moore | Ó Mórdha | descendant of Mórdha, 'majestic' | Laois |
Ranking from Wikipedia's list of most common surnames in European countries. It counts a name and its prefixed forms together — Sullivan and O'Sullivan are one name — which is why the order can differ from lists that separate them.
Ireland ran out of ancestors before it ran out of people. Surnames here were fixed early — from the tenth century, far earlier than most of Europe — and each one was formed from a single man's given name. Because the same given names were popular everywhere, the same surname was invented independently in several places: there are three unrelated Murphy septs and six royal O'Connor lines. Then anglicisation flattened dozens of distinct Irish names into one English spelling. The result is a country where a handful of surnames cover an extraordinary number of unrelated families.
Which is worth remembering before you claim a chief: sharing a surname with a king is not the same as descending from one.
All 285 surnames A–Z · Every surname in Irish · The surname map · Ó and Mac explained