The origin of the names comes from Firghil (Ó Fearghial or Fergal), a descendant of Eoghan, (son of Niall Noígíallach, the most prolific warrior in Irish history) brother of St. Columcille, and are thus nearest in descent to Columcille.
The leading line of the family were hereditary coarbs of Kilmacrennan, County Donegal.
The Chief of the Name possessed the hereditary right of inaugurating O'Donnell as lord of Tirconnell.
Statistics relating to the modern distribution of the population indicate that the name is seldom met with outside County Donegal and contiguous areas.
The name is very closely associated with the north Donegal, especially Fanad and surrounding areas.