The surname O'Halloran is of Irish origin, stemming from the Gaelic name Ó hAllmhuráin, meaning "descendant of Allmhurán." The personal name Allmhurán is believed to be derived from "allmhurach," meaning "foreigner" or "stranger," likely referring to someone who came from abroad or was associated with foreign places or peoples. Historically, the O'Halloran family was part of the ancient Gaelic nobility in Ireland and belonged to the Dál gCais tribe. They were mainly located in County Clare and were prominent in the west of Ireland, particularly in the region around Galway. The O'Halloran's were influential in medieval Ireland, with many serving as chieftains.