There are 2 McGrath Clans in Ireland. One originates from the ancient kingdom of Thomond in the south west whilst the other hails from Ulster in the north east. There is evidence that members from both of these have intermarried. A specific example is Miler McGrath (1523-1622) from the Ulster region who eventually became the Archbishop of Cashel in Tipperary.

It is known that the various McGrath Clans of Ireland originated at Isle Mcgrath in Co Clare where they have been traced from the 11th Century. They also shared the history of the site from the late Bronze Age when settlers from Scandinavia colonized the area along the Fergus Estuary adjacent to Clare Abbey outside Ennis.

The McGrath family name is derived from the name Macraith which is borne by the descendants of four distinguished septs who had their common origin in the Kingdom of Thomond in present day County Clare. There are at least seven McGrath septs in Ireland today but only four of them originate from Clare. The McGraths of Pettigo, Co. Donegal, the McGraths of Co. Tipperary and the McCraghs of Co. Waterford are all descended from the Macraiths of Isle McGrath in Thomond (McGraw, 2005). Three of the four septs are in the south of modern Eire whereas Donegal is in the north-west but is not part of Ulster. The other three have adopted the name independently. The term clan means a traditional kinship group sharing a common surname and heritage and existing in a lineage based society prior to the 17th Century (McCraw, 2005)

See the History of Clan McGrath page for more.