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O'Mahony

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About us

Welcome to the O Mahony yDNA project. Ta failte romhat. 


There are a great many O Mahonys in Ireland—the name is included, usually without the prefix O, among the hundred commonest Irish surnames. It belongs almost exclusively to West Munster. The vast majority of Mahony and O Mahony births are registered today in Co. Cork, the area historically associated with the sept.

O Mahony chieftains were powerful, often described as princes. Their principal territory comprised the modern barony of Kinelmeaky and extended to the sea, with some fourteen castles on the coast of southwest Cork. The name O Mathghamhna—in modernized spelling O Mathuna—is derived from Mathghamhain (Irish for bear), the grandson of Brian Boru. Mathghamhain was killed, with many more of the Desmond fighting men, at the Battle of Clontarf in 1014. (Edward MacLysaght, Irish Families and Diarmuid O Murchadha, Family Names of County Cork)

It must be remembered that Cian derived his yDNA from his father who was a member of the Eoghanacht Rathlind (not from the O Brien side of the family) so the O Mahony yDNA is distinctly different from that of the O'Briens. 

The O MAHONY Surname DNA project was begun on 1 August 2003 by Perry Streeter and was transferred in early 2007 to the O Mahony Society for ongoing administration. It is currently administered by Dr. Finbar O'Mahony.