Two native Irish families adopted the name. The first was based on the borders of the modern counties of Donegal and Fermanagh, around Termon MacGrath, and were erenaghs (hereditary abbots) of the monastery of St. Daveoc on Lough Derg. Castle Magrath, dating from the 16th century, stands in Pettigo in Co. Fermanagh. The most remarkable bearer of the name was of this family, Meiler Magrath (1523-1622), who managed to be, simultaneously, Catholic Bishop of Down and Connor and Protestant Archbishop of Cashel. His rapacity was notorious, and he held six Anglican bishoprics, four of them at the one time, as well as the income of seventy parishes. For his pains, he lived to be 100.
The other family were originally based in Co. Clare, where they were famous as hereditary poets and genealogists to the ruling O'Brien family of Thomond. One of this family John Mac Cratih wrote the eleventh-century history The Wars of Turlough.
Today neither area has large numbers of the surname. The southern family spread eastwards, into counties Tipperary and Waterford, while the northern family's descendants are now mainly to be found in Co. Tyrone, where they settled around Ardstraw after being driven from their homeland by the O'Donnells.
Descendants of the Clare family were responsible for the famous bardic school at Cahir in Co. Tipperary which lasted down to the eighteenth century.
Joseph McGrath (1877-1966) was involved in the 1916 rising and became Minister for Labour and subsequently Minister for Industry and Commerce in the new Irish government. He went on to a successful business career, founding a dynasty which continues to the present.
Sir Patrick Thomas Magrath (1868-1929) was descended from the Waterford family. He became President of the Upper House of the Newfoundland legislature.
Andrew Condon Magrath (1813-1893), son of refugee from the 1798 rebellion, fought on the Confederate side in the American Civil War, and went on to become Governor of South Carolina.
James Magrath (1835-1898) of the Tipperary family was an Oblate Missionary, and became the first Provincial of the Oblate Fathers in the U.S.A.