Very numerous: all provinces but primarily Donegal and adjoining counties. MacLysaght mentions 23 different spellings of the anglicised name! The Irish is Ó Gallchobhair, meaning "lover of foreigners". They were a leading sept of Cineál Conaill and ally of the O'Donnells. The sermons of Bishop James O'Gallagher (1681-1751) are one of the treasures of Irish spirituality. The name has been abbreviated to Gallahue. IF & SGG.
Quite numerous: Ulster generally. Ir. Ó Gallchóir. See Gallagher.
Very rare: Ulster. Ir. Ó Gallchobhair, Ó Gallchóir. See Gallagher.