"Mac Giolla Naomh," meaning "son of the devotee of the saints" was an Irish clann or sept that originated in southern Connemara, Connacht.
Over the years, however, "Mac Giolla Naomh," which was incorrectly transcribed as Mac Giollarnáth, and then erroneously translated as Ford (surname) or Forde, from the resemblance of the final syllable to Áth, a ford (crossing).
[1] Lastly, in County Cork and County Waterford, the name was an Anglicised version of Ó Fuaráin, meaning "descendant of Fuarthán".
[2] The personal name Fuartháin, derived from the Irish language word fuar (meaning "cold"), was once taken to represent the Irish word fuarathán (meaning "cold little ford"), which led to the surname being translated as Ford (surname) or Forde although more often it was Anglicised as Foran.
The ancestor of Henry Ford (USA) came from County Cork in 1847.