Regan, ó Riagáin, ó Réagáin A Gaelic surname meaning descendant of Riagáin, which personal name meant ‘little king’. A sept of Meath who were a branch of the southern Uí Néill and one of the four tribes of Tara. They were lords of south Breagh, but were dispossessed shortly after the Cambro-Norman invasion. A sept of Thuas Mhumhan (Thomond), said to be descended of Riagán, son of Donncuan, a brother of Brian Boru. In 1890 Regan was the sixty-sixth most numerous surname, the estimated number of bearers was 10,500 and the surname was chiefly found in Cork, Roscommon and Mayo. In the United States Reagan is the 2,000th most numerous surname with an estimated 16,500 bearers. It is numerous in the state of Massachusetts.
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