Origins, meanings, and the county roots of Ireland's most common family names
Irish surnames carry centuries of history in a single word. Most derive from the Gaelic naming system that flourished in Ireland before the Norman conquest — a system built on ancestry, occupation, and place. The O' prefix (Ó in Irish) means "grandson of" or "descendant of." The Mac prefix means "son of." Together, they gave rise to the surnames carried today by tens of millions of people around the world.
The great dispersal of the nineteenth century — famine emigration, economic migration, the gradual hollowing-out of rural Ireland — sent these names to every English-speaking country. Today there are more people of Irish descent living outside Ireland than in it. The surnames travelled with them, often anglicised, sometimes altered beyond recognition, always carrying the same root.
Below: the fifty most common Irish surnames, with their Gaelic originals, meanings, and the counties where they are most concentrated.
The most common surname in Ireland. The name derives from muir (sea) and cath (battle). Murphys are most densely concentrated in County Cork and County Wexford, where the sept originated.
Cork · WexfordCeallach meant "bright-headed" or possibly "strife." One of Ireland's most widely distributed surnames, found in every province. The sept originated in County Galway, where the Uí Maine kingdom thrived.
Galway · MeathDescended from Brian Boru, High King of Ireland, who died at the Battle of Clontarf in 1014. One of the most distinguished surnames in Irish history, concentrated in County Clare and Munster.
Clare · TipperaryRian likely meant "little king." The Ryan sept originated in County Tipperary and remains most concentrated there, though the name is found throughout Leinster and Munster.
Tipperary · LimerickUnlike most Irish surnames, Walsh is not of Gaelic origin. It was given to Welsh settlers who came to Ireland with the Norman invasion in the twelfth century. Now one of the most common surnames in Connacht.
Galway · MayoWhile Smith is English in origin, many Irish Smiths are anglicisations of Mac Gabhann (Cavan/Monaghan) or Mac Gowan. The blacksmith was a figure of high status in Gaelic society.
Cavan · MonaghanOne of the great Munster surnames. The O'Sullivans were lords of Beare and Bantry in County Cork before the Elizabethan confiscations. Still most concentrated in Kerry and west Cork.
Kerry · CorkThe Powers came with the Normans, from the French le Poer (the poor, in the feudal sense of modest means). They became one of the great Norman-Irish families of County Waterford.
Waterford · WexfordConchobhar was a personal name meaning "lover of hounds." The O'Connors of Connacht were kings of the province; O'Connor Faly ruled Offaly. Several distinct septs share the name.
Roscommon · OffalyNiall of the Nine Hostages, the semi-legendary High King, is the ancestor from whom the O'Neills trace their descent. The Ulster O'Neills were among the last Gaelic lords to resist English rule.
Tyrone · AntrimThe O'Reillys were kings of Breifne (modern Cavan), one of the most powerful Connacht kingdoms. The name is common throughout Ulster and Leinster in its various anglicised forms.
Cavan · LeitrimBran meant "raven." The Byrnes were chiefs of Crioch Branach (Wicklow), driven into the mountains by the Normans in the twelfth century. One of Leinster's most prominent Gaelic surnames.
Wicklow · DublinDonnchadh meant "brown warrior." The O'Donoghues were lords of Lough Lein in Kerry before the Norman period. The name remains most concentrated in Munster.
Kerry · CorkCarthach meant "loving." The MacCarthys were the dominant dynasty of Munster, descended from Eoghan Mór, legendary king of Munster. Centred in Cork and Kerry.
Cork · KerryFrom gallchobhar, meaning "eager aid" or "zealous helper." The Gallaghers were lords of Tír Chonaill (Donegal), hereditary marshals of the O'Donnell clan army.
DonegalThe Dohertys were one of the principal septs of Inishowen in County Donegal. The name's meaning may refer to someone who was "harmful in battle." Among the most common names in Ulster.
Donegal · DerryFrom ceann (head) and éidigh (armoured), referring to a helmet. The Kennedys were a Dalcassian sept from County Tipperary, kinsmen of the O'Briens — and ultimately of President John F. Kennedy.
Tipperary · ClareFrom loingseach, meaning "one who is exiled" or "mariner." Lynch was one of the Tribes of Galway — the fourteen merchant families who dominated Galway city in the medieval period.
Galway · ClareMuireadhach may mean "lord" or derive from muir (sea). Several distinct septs bear this name across Connacht and Ulster. Also common among Scottish planters in Ulster.
Roscommon · DownConn was a common personal name, possibly meaning "wisdom" or "chief." The principal Quinn sept was from Antrim; others arose in Longford and Clare. A surname found throughout Ireland.
Antrim · TyroneMórda meant "stately" or "noble." The O'Moores were kings of Laois (then called Leix), one of the most powerful Leinster kingdoms. The Gaelic surname is now usually found as Moore.
Laois · OffalyFrom dubh (dark/black) combined with the Norse personal name Ivar. The O'Dwyers were lords of Kilnamanagh in County Tipperary. A name that reflects Viking-Gaelic cultural fusion.
TipperaryBraonán meant "moisture" or "drop." Several distinct Brennan septs arose independently across Ireland — in Kilkenny, Roscommon, and Fermanagh. The name is widely distributed as a result.
Kilkenny · RoscommonFrom flann, meaning blood-red or ruddy. The Flanagans were lords of Connacht, with the principal sept in County Roscommon. A name found throughout Connacht and Ulster.
Roscommon · FermanaghSéaghdha may have meant "hawk-like" or "stately." The O'Sheas were a powerful Kerry family and remain most concentrated in that county today. The name is sometimes anglicised as Shea.
KerryFrom uiginn, derived from the Norse word for "Viking." The Higgins family were hereditary poets in Connacht, one of the great learned families of medieval Ireland.
Sligo · MayoFrom fear (man) and gal (valour, vigour). The O'Farrells were kings of Longford (Annaly), one of the strongest kingdoms in Leinster. The name remains common in the midlands.
Longford · WestmeathDiarmaid was a common personal name of uncertain origin, perhaps "without injunction" or "free man." The MacDermotts were lords of Moylurg in County Roscommon, one of the royal families of Connacht.
RoscommonThe Burkes (also Bourke) are descended from William de Burgo, who came to Ireland with Strongbow. They became so thoroughly Gaelicised that they led Connacht resistance against later English rulers.
Galway · MayoDescended from Ceallachán of Cashel, King of Munster who died in 954. The O'Callaghans were lords of Pobail Uí Ceallacháin in County Cork. Still most common in Munster.
Cork · LimerickFrom dubh (dark) and gall (foreigner), a term used for Danish Vikings. The Doyles are most heavily concentrated in Leinster, particularly Wicklow and Wexford.
Wexford · WicklowFrom con (hound) and mara (sea). The MacNamaras were the second most powerful family in Thomond, hereditary marshals to the O'Brien kings of Clare.
ClareDomhnall meant "world-mighty." The O'Donnells were lords of Tír Chonaill (Donegal) — among the last great Gaelic ruling families. Their exile in the Flight of the Earls in 1607 ended the Gaelic order.
DonegalNuallán meant "famous" or "noble." The O'Nolans were lords of Foharta in County Carlow. The name spread throughout Leinster and is now most common in Carlow and Dublin.
Carlow · DublinFrom donn, meaning brown-haired or dark. The O'Dunnes were chiefs of Iregan in County Laois, one of the great Leinster families. The name is now found throughout the midlands.
Laois · OffalyOne of the few Fitz- names of Gaelic origin rather than Norman. The MacGiollaPhádraigs were lords of Upper Ossory in County Laois. Fitzpatrick is the anglicised form adopted after the seventeenth century.
Laois · KilkennyRuarc was a personal name possibly meaning "champion." The O'Rourkes were kings of Breifne (Leitrim/Cavan), one of Connacht's most powerful dynasties. Dervorgilla, wife of O'Rourke, played a central role in the Norman arrival.
Leitrim · CavanThe meaning of Baoigheall is uncertain, possibly related to "vain pledge." The O'Boyles were lords of Tír Baoigheallaigh in Donegal, a territory named for their ancestor.
DonegalFlemings came to Ireland from Flanders with the Normans. They settled principally in Meath and Connacht, where many became thoroughly Gaelicised. The name refers to their Flemish origin.
Meath · LouthCathán meant "battle." The O'Kanes (or Keanes) were lords of the territory between the Bann and Foyle rivers in Ulster, one of the principal septs of Derry.
Derry · GalwayFrom dubh (dark) and the River Sláine (Slane). The O'Delaneys were lords of a territory in County Laois near the River Slane. The name is most common in Laois and Kilkenny.
Laois · KilkennyFrom foghlaidhe, meaning plunderer or pirate. The O'Foleys were lords in Waterford and remain most common in Munster. The name reflects the seafaring traditions of the southern coast.
Waterford · CorkA senior branch of the McCarthy dynasty and the paramount chieftain of Desmond. The MacCarthy Mór title was used by the Lords of Carbery until the Elizabethan period. Centred in County Cork.
CorkFrom mathghamhain, meaning "bear." The O'Mahonys were lords of Kinelmeaky in County Cork and one of the oldest Munster families. Related to the MacCarthys through common Eoghanacht ancestry.
CorkFrom anlu, meaning "great champion" or "great warrior." The O'Hanlons were lords of Orior in County Armagh, one of the principal septs of Ulster. The name is most common in Armagh and Down.
Armagh · DownFrom odhar, meaning dun or sallow-coloured. The Maguires were lords of Fermanagh and one of the great Ulster dynasties. Hugh Maguire died in 1600 fighting the English in the Nine Years' War.
FermanaghThe Dillons came from Brittany with the Normans and settled in Westmeath and Roscommon, where they became one of the great Norman-Irish families. The Dillon title survives as an Irish viscountcy.
Westmeath · RoscommonFrom éilidhe, meaning claimant or ingenious. Two distinct septs — one in Cork, one in Sligo — produced this surname independently. Now common throughout Munster and Connacht.
Cork · SligoFrom madra (dog, hound). The O'Maddenes were lords of Síol Anmchadha in County Galway. The name is most common in east Galway and south Roscommon.
GalwayLove Ireland is a daily newsletter about Irish culture, history, and the places that made the diaspora who it is. 64,000 readers, from Dungarvan to Chicago.
Read Love Ireland →The two most recognisable markers of Irish surnames are the prefixes Ó (anglicised as O') and Mac (also written Mc or M'). Both indicate descent — but from different relationships.
Ó means "grandson of" or, more broadly, "descendant of." When Brian Boru's descendants became the O'Briens, they were signalling their descent from Boru through the paternal line. The accent over the O in Ó indicates a long vowel — it is not an apostrophe, though English usage has treated it as one for centuries.
Mac means "son of." MacDermott means son of Dermott (Diarmaid). MacNamara means son of the hound of the sea. In practice, Mac surnames were inherited just like O surnames — the "son of" became fixed rather than reapplied each generation.
Both prefixes were systematically suppressed during the sixteenth and seventeenth centuries under English rule. Many families dropped the prefix entirely. The revival of Irish cultural identity in the nineteenth and twentieth centuries saw many families restore the O' or Mac — but not all did, which is why you find both Kelly and O'Kelly, Sullivan and O'Sullivan.
Many Irish surnames are strongly associated with specific counties because Gaelic Ireland was organised into territorial septs — extended kin groups who held land in defined areas. A sept's surname became concentrated in the territory it controlled, and while emigration and plantation disrupted this pattern, the association often remains visible in surname distribution data today.
The 1890 surname survey conducted by Robert Matheson for the Registrar-General of Ireland is still the most comprehensive mapping of Irish surname distribution by county. Many genealogists begin their research by identifying the county associated with a surname — it can narrow a family search from 32 counties to one or two.
If you're researching Irish ancestry, the county of origin is often the most valuable single piece of information you can establish.
There are approximately 33 million Americans who claim Irish descent — more than six times the population of the Republic of Ireland. The Irish surnames carried to America arrived in several distinct waves.
The first large wave came with the Scotch-Irish (Ulster Presbyterians) in the eighteenth century. Names like McKinley, Wilson, Jackson, and Polk entered American political history through this community. The second and far larger wave came with the Famine emigration of 1845–1852, which brought the O'Briens, Murphys, Kellys, and Sullivans of Massachusetts, New York, Pennsylvania, and Illinois.
At Ellis Island and earlier ports, many surnames were simplified or altered. Ó Treasaigh became Tracy. Ó Maolalaidh became Molloy. Mac Giollapadraig became Fitzpatrick. Some changes were errors; others were deliberate attempts to fit names to an English-speaking world.
The result is that the same Gaelic root can appear in modern America under a dozen different spellings — and tracing the path from Murphy to its townland of origin in Cork requires navigating a century and a half of records on both sides of the Atlantic.
Love Ireland publishes every morning. Essays about specific places, specific people, specific moments in Irish history. No listicles. No filler. 64,000 readers who know the difference.
Start Reading Free →