Having evolved over the centuries to be the surnames we recognise today, Irish last names have a rich and vibrant history. In early times, when Ireland had a much smaller population and mass movement of people was uncommon, it was not unusual for people to be known by only one name. However, as the population began to grow in the Middle Ages, the Gaelic Clann system was established in Ireland to give people a shared identity with their people of the tribe and the area from which they came.
While many Irish surnames have evolved from Gaelic to English over hundreds of years, many traditional Irish names remain common across Ireland today. So, here are the most popular last names for every county of Ireland.
1. Antrim – Smith
Smith is not just Antrim’s most popular name, but it is also the most common name in Europe.
The name derives from the Old English smið or smiþ, meaning “one who works in metal”, thus indicating that the owner of this surname would have been a metal worker or blacksmith.
2. Armagh – Campbell
The most popular surname in Armagh is Campbell, which is derived from the Gaelic terms “cam” and “beul”, meaning “crooked mouth” or “wry mouthed”.
3. Carlow – Mullins
An anglicised form of the Irish O’Maolain, the popular Carlow surname Mullins is thought to be derived from “maol” meaning “bald”.
4. Cavan – Brady
The Irish surname Brady is derived from the Gaelic surname Ó Brádaigh or Mac Brádaigh and means “spirited and broad”.
5. Clare – MacMahon
MacMahon, from the Old Irish Mac Mathghamhna, means “son of the bear” or “son of the bear-calf”.
6. Cork – O’Connor
One of the most popular last names for every county of Ireland, O’Connor, derives from the Gaelic Ó Conchobhair, meaning “grandson/descendant of Conchobar”.
The Irish given name Conchobhair means “lover of hounds”.
7. Derry – Bradley
An English surname meaning “broad wood” or “broad meadow” in Old English, Bradley is also an anglicisation of the Gaelic Ó Brolacháin from County Tyrone.
8. Donegal – Gallagher
Gallagher has been a popular family name in Donegal since as far back as the 10th-century when the Gallagher (or Gallchobhair mac Rorcan) family ruled the Tir Chonaill county.
9. Down – Thompson
The surname Thompson is not only popular in Ireland but also across England, Scotland, and Wales.
A patronymic surname of Scottish origin, Thompson means “son of Thomas”.
10. Dublin – Byrne
In the Irish language, Byrne translates as Ó Broin and means “descendant of Bran”.
The name has been traced back as far as the ancient Celtic chieftain, Bran mac Máelmórda, King of Leinster, who was deposed in 1018.
11. Fermanagh – Maguire
The Irish surname Maguire comes from the Gaelic Mac Uidhir, meaning “son of the dun or dark coloured one”.
12. Galway – Kelly
The popular Galway surname Kelly comes from the Gaelic O’Ceallaigh, which means “bright headed” or “troublesome”.
13. Kerry – O’Sullivan
The surname O’Sullivan derives from the Sullivan clan, an Irish Gaelic clan based in what is today County Cork and County Kerry.
It is interpreted as “little dark-eyed one”.
14. Kildare – O’Toole
The O’Tooles were historically one of the most powerful families in Leinster, and the translation of the Irish name means “descendant of the mighty people”.
15. Kilkenny – Brennan
The most popular Irish surname in Kilkenny, Brennan, is an anglicised form of three different Irish surnames: Ó Braonáin, Mac Branáin and Ó Branáin.
This patronymic surname means “son of Branán”, a personal name meaning “little raven”.
16. Laois – Dunne
Dunne is one of the most popular last names for every county of Ireland.
This Irish surname is derived from the Irish Ó Duinn and Ó Doinn, meaning “dark” or “brown.”
17. Leitrim – Reynolds
In Gaelic, the name Reynolds is Mac Raghnaill, which comes from the Old Norse name Rognvald.
The patronymic surname meaning “son of Reynold” derives from the given name meaning “powerful ruler”.
18. Limerick – Ryan
In some cases, Ryan is a shortened form of the patronymic name O’Ryan, an anglicised form of the Gaelic surname Ó Riain.
In Irish, Ryan is thought to mean “king”, “water”, or “ocean”, and is today among the top ten most common surnames in Ireland.
19. Longford – O’Reilly
O’Reilly is a name of Gaelic origin deriving from the kings of East Bréifne in what is today County Cavan.
O’Reilly is the patronymic form of the Irish name Reilly, which means “extroverted one”.
20. Louth – Matthews
Matthew is a variant of the Gaelic name MacMahon, meaning “son of Matthew”.
21. Mayo – Walsh
Walsh is an Irish surname that means “Briton”, “foreigner”, or literally “Welshman”.
It is a name that was brought to Ireland by Welsh, Cornish, and Cumbrian soldiers during and after the Norman invasion of Ireland.
22. Meath – O’Farrell
O’Farrell is the most common Irish last name in County Meath. It derives from the Gaelic O’Fearghail, which means “man of valour”.
23. Monaghan – Connolly
Connolly is the anglicised form of the Old Gaelic O’Conghaile, which means “fierce as a hound or wolf”.
24. Offaly – Hennessy
Hennessy is the anglicised form of the Gaelic name Ó hAonghusa, which came from the Irish Kingdom of Uí Failghe or modern-day County Offally.
25. Roscommon – McDermott
McDermott derives from the Gaelic Mac Diarmada, which means “son of Diarmuid” or “free man”.
This Irish name comes from Tadhg mac Diarmata, who was King of Connacht before the Norman invasion.
26. Sligo – McGinn
The anglicised form of the Gaelic Mag Finn, McGinn means “son of Fionn”.
Variations of the name include McGinne, Ginn, McGing, Ging, McKing, and Maginn.
27. Tipperary – Purcell
Purcell is an Irish name of French or Norman origin, which was given to those whose occupation was tending to pigs.
28. Tyrone – O’Neill
One of the most popular last names for every county of Ireland is O’Neill.
An anglicisation of the Gaelic Ua Néill, meaning “son of Niall”, an Irish name that means champion.
29. Waterford – Power
The Irish surname Power actually derives from Norman or French origin as it was brought to Ireland during the Anglo-Norman invasion of the late 12th-century.
From the French word, povre, Power means poor or pauper.
30. Westmeath – Lynch
The most popular surname in Westmeath, Lynch, derives from the Gaelic Ó Loingsigh, meaning “son of Loingseach”.
The given name Loingseach means “having or belonging to a fleet of ships”, thus indicating that the owner of this name would have been a mariner or seaman.
31. Wexford – Murphy
One of the most well-known Irish surnames, Murphy, is the most popular last name in Wexford.
The Gaelic equivalent of this anglicised surname is Ó Murchadha, and it means “sea battler”.
32. Wicklow – Cullen
The surname Cullen is of Gaelic origin, and it is believed to be derived from the pre-8th-century Old Gaelic name O’ Cuileannain or Ó Cuilinn, meaning “son of Cuilleannain”.
Do your Irish ancestors have any of the surnames listed above? Add their profile to the IrelandXO Ancestor Chronicles and help other descendants from the same family discover more about their Irish ancestry and the place in Ireland where they come from.