Below are some common Irish surnames and their meanings

Casey - Ó Cathasaigh

Ó Cathasaigh, meaning descendant of the vigilant one. The name was associated with a number of counties including Cork, Dublin and Fermanagh.

Daly - Ó Dálaigh

The Dalys were a learned Irish bardic family. They first came to prominence early in the twelth century, when Cú Connacht Ó Dálaigh was described as ‘The first Ollamh [professor] of poetry in all Ireland.’

Dempsey - Ó Diomasaigh

Ó Diomasaigh, descendant of Díomasach, means proud. The family originated in the Laois Offaly area and in the 12th century, O’Dempsey, Chief of Offaly, was one of the few Irish chieftains who defeated Strongbow.

Donnelly - Ó Donnaile

The descendant of Donnghaile probably meaning a warrior with brown hair. The Donnelly clan was originally a division of the Cineál Eoghain. Donnghaile O'Neill, who died in 876, was a direct descendant of Eoghan.

Flanagan - Ó Flannagáin

The Flanagan family is descended from Flannacán Mac Fógartach, the word flann meaning red or ruddy. They were chiefs of Toorah or Tuath Rátha in County Fermanagh and were possibly based in the parish of Donaghmoyne.

Kelly - Ó Ceallaigh

Kelly is the second most common surname in Ireland. It derives from various native surnames including Ó Ceallaigh and Ó Cadhla. The former is the most common source and comes from the first name Ceallach probably meaning frequenter of churches. One of the most famous chieftains of the clan was Tadhg Mór Ó Ceallaigh, who was killed in the Battle of Clontarf in 1014.

McKenna - Mac Cionnaith

Mac Cionnaith, the name is also spelt Mac Cionaodha or, meaning ‘son of Cionaodh’. 'Cion' means respect and affection in Irish, and Aodh, is a first name. Aodh was originally the name of the Celtic god of fire. The personal name Cionaodh probably means 'beloved of Aodh'. Like then McMahon family, the McKennas are associated with Truagh, County Monaghan, where they were ‘The Lords Of Truagh’.

McLaughlin - Mag Lochlainn

The name Lochlann in Irish means ‘of the lakes’, and refers to the Vikings who came from the fjords of West Norway. Originally belonging to the Cineál Eoghain, the McLaughlins were closely related to the O'Neill dynasty. Two kings of Ireland came from the clan, Domhnall Ua Lochlainn and Muircheartach Mac Lochlainn.

McMahon - Mac Mathúna

The McMahon surname arose separately in two areas, in west Clare and in Co. Monaghan. In Thomond the MacMahons were part of the the Dál gCais group. They claimed decent from Mahon O'Brien who was grandson of Brian Ború. The Oriel MacMahons were based in Truagh, north Monaghan. They ruled the kingdom of Oriel between the thirteenth and the sixteenth centuries.

Monaghan - Ó Manacháin

The Monaghans are descended from the warrior Manachán who was mentioned by the Four Masters in the year 866. The name Manachán itself means 'little monk'. Chieftains in Co. Roscommon, until the year 1249, the Monaghans were ousted by the O'Beirnes.

Moore - Ó Mórdha

Descendant of Mórdha, meaning ‘stately and noble’. The Anglo-Norman Moore family who became established in Munster after the Anglo/Norman invasion are called de Móra in Irish. The name is derived from the word English word ‘moor’. Rory O’Moore was an Irish landowner of ancient lineage, and was one of the main organisers of the 1641 Rising.

Murphy - Ó Murchú

Murphy is the most common surname in Ireland. It is the English version of two indigenous surnames Ó Murchú and Mac Murchaidh. The name derives from the Irish personal name Murchadh meaning 'one who battles at sea'. The Murphy clan of Leinster were based in County Wexford.

O'Donnell - Ó Dónaill

The surname derived from the first name Domhnall, meaning 'ruler of the world'. The O’Donnells were an ancient and powerful Irish family who as princes of Tír Chonaill or Donegal were at various times allies and rivals of the powerful O’Neill dynasty.

O'Farrell / Farrell - Ó Fearail

The O’Farrell clan can trace its origins to the battle of Clontarf in 1014. They are the descendants of Fearghal, who fought alongside Brian Boru at the battle of Clontarf. The Uí Fhearghail went on to become princes of the territory of Annaly (Anghaile), in the vicinity of present day County Longford.

O'Kane - Ó Catháin

The O’Kanes were descended from Eoghan, son of Niall of the Nine Hostages. In the late Middle Ages, they held the privilege of inaugurating the Chief of the Uí Néill by tossing a shoe over the new Chief's head to denote they accepted his rule. They ruled from Dungiven Castle.

O'Neill - Ó Néill

It is believed that the O’Neill surname derives from Niall Glúndubh, who was king of the Cenél nEoghain and High King of Ireland in the 10th-century rather than from their ancestor, Niall of the Nine Hostages.

O’Connor - Ó Conchobhair

Descendant of Conchobhar. There was a number of disctinct O’Connor families, located in Derry, Sligo/Roscommon, Offaly/Laois and Clare and Kerry. In Derry they were based in the Dungiven area and were the most powerful sept of the Cianachta, but were subsequently overthrown by the O’Kanes.

O’Doherty / Doherty - Ó Dochartaigh

The Doherty family are named after Dochartach who was a member of the Cineál Conaill dynasty in the tenth century. Later chiefs of the clan were called the Lords of Inishowen.

O’Reilly - Ó Raghallaigh

The O’Reilly family were associated with Cavan and they built a castle in the town in the thirteenth century. The term ‘life of Reilly’ is believed to refer to this family as they became very wealthy after establishing a market in the town.

Smith - Mac Gabhann

Although many English and Scottish settlers named Smith arrived in Ireland during the Plantation, the indigenous surname Mac Gabhann, or son of the blacksmith existed here prior to this time. Confusion has arisen however, as Mac Gabhann has often been anglicised as Smith.