From Ó Ceallacháin, ‘descendant of Ceallachán’ — named for a tenth-century King of Munster whose line once ruled from Cashel itself.
The O’Callaghan certificate.
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Gaelic Origin · Root name Ceallachán
O'Callaghan descends from Ceallachán Caisil, King of Munster and head of the Eóganacht dynasty, who ruled from the Rock of Cashel until his death in 954. His descendants, the Uí Cheallacháin, held that royal ground for generations before the Anglo-Norman advance pushed them west.
Displaced from Cashel, the family rebuilt as lords of their own smaller territory around Duhallow in north Cork — proof that losing a throne didn't mean losing a name, or the land under it.
Irish form: Ó Ceallacháin
