Surname comes from the Irish Mathgamha or MacMathúna meaning bear.
There are two distinct septs, the main one being from Clare. Mahon was
the son of Murtagh Mor O'Brien who was king of Ireland. He died in 1119.
The last inaugurated chief of the name fell at Kinsale in 1602. The
Ulster sept were lords of Oriel . They came to prominence with the
decline of the O'Carrolls. Bernard (1680 - 1747), his uncle Hugh who
died in 1737 and his brother Ross Roe (1698 - 1748) were all archbishops
of Armagh. They had previously been bishops of Clogher. Three out of
five bishops who held the see of Clogher were McMahons. Heber McMahon
(1600 - 1650) was a leader of the confederate Catholics. He commanded
the Ulster army and died on the scaffold.Hugh, the last chief of the
Ulster sect, was betrayed by Owen O' Connolly and beheaded in 1641. Col.
Brian McMahon fought at Benburb and was on the supreme council of
confederate Catholics. The name was also prominent in King James' Irish
army. Col. Art McMahon's infantry regiment was notable in France's Irish
brigade. John McMahon (1715 - 1780) was born in France.