The top 100 Irish last names explained

Find out more about your Irish roots and where your family name hails from

Redmond - Réamonn. A Hiberno-Norman family of importance throughout Irish history. They are associated almost entirely with South Wexford. The branch of the MacMurroughs in north of that county, some of whom adopted the name of Redmond whose chief was called Mac Davymore, are quite distinct from the MacRedmonds.

(O) Regan - Ó Riagain. Ó Réagainis used in county Waterford. There are three septs with this name. That shown as of Leix was in the early times one of the ‘Tribes of Tara’. The eponymous ancestors of the Thomond sept were akin to Brian Boru. The third was akin to the MacCarthys.

(O) Reilly - Ó Raghailligh One of the most numerous names in Ireland, especially so in Co. Cavan. The prefix O has been widely resumed in the anglicized form. The head of this important sept was chief Breffny O’Reilly

(O) Riordan - Rearden Ó Riordáin. This numerous sept belongs exclusively to Minster, he earlier form of Ó Rioghbhardáin reveals its derivation from riogh bhard, royal bard.

(O) Rooney - Ó Ruanaidh. Originating in Co. Down, where Ballyroney locates them, this name is now numerous in all the provinces except Munster. In West Ulster and north Connacht Rooney is often an abbreviation of Mulrooney.

(O) Shea - Shee  Ó Séaghdha; mod. Ó Sé (séaghdha, hawklike, secondary meaning stately). Primarily a Kerry sept, but (as in Shee) it is notable as the only Gaelic-Irish name among “the Tribes of Kilkenny’ to which county and Co. Tipperary a branch of the sept migrated in the thirteenth century.

(O) Sheehan - Sheahan Ó Síodhacháin. (The obvious derivation from síodhach, peaceful, is not accepted by some Celtic scholars). The Dalcassian sept which spread southwards accounts for the majority of Sheehans who are now very numerous in Co.s Cork, Kerry, and Limerick. Formerly also there was an Uí Maine sept of this name which, however, is rarely found in Connacht today.

(O) Slattery - Ó Slatara, Ó Slatraigh (slatra, strong). Of Ballyslatterly in east Clare. The name has now spread to adjacent counties of Munster.

Smith - Smyth  When not the name of an English settler family, Smith is usually a synonym of MacGowan, nearly always so in Co. Cavan.

(Mac) Spillan(e) -  Mac Spealáin (derivation as O’Spillane). The family is, however, quite distinct from Ó   Spealáin (O’Spillane) Spollan and Spollin, rarely retaining the prefix Mac, are numerous in County Offaly. Older anglicized forms were Spalane and Spalon.

(O) Sullivan - Ó Súileabhain. (While there is no doubt that the basic word is súil (eye) there is a disagreement as to the meaning of the last part of the name). This is the most numerous surname in Munster and is third in all of Ireland. Originally of south Tipperary, the O’Sullivans were forced westwards by the Anglo-Norman invasion where they became one of the leading septs of the Munster Eoghanacht. There were several sub-septs, of which O’Sullican Mor and O’Sullivan Baere were the most important.

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