O'Domhnaill

 (Modern: O'Donnell)
County of Origin: Donegal

Meaning: Descendant of Domhnall (Donal), The name derived from dubno 'world' and val- 'might, rule'.

The first clan head, Domhnall, died 901, claimed direct descent from Niall of the Nine Hostages. The sept was dominant in the territory of Tyrconnell (modern County Donegal)