This sept, or clan, is a branch of the southern Ui Neills. The name is found mainly in Co. Monaghan but is also numerous in Leinster. In Irish the name means son of Cionnaith. Despite being one of the most common surnames in Ireland, little is known about the origins of the family.

Among the famous bearers of the name is the actress Siobhan McKenna(1923-1986). She was born in Belfast and became one of the most outstanding Irish actresses of her generation. Another foremost contemporary actor is T. P. McKenna, who was born in Mullagh, near Virginia, Co. Cavan, in 1929.

A McKenna figure of note in history was General Juan MacKenna, who was born in Ireland in 1771. Where he was born remains something of a mystery; some sources claim he was born just outside Monaghan town, the true home of the McKennas, while others say that he was born in Clogher, Co. Tyrone. He was a famous soldier of fortune in Chile but died in 1814 in Buenos Aires, where he is buried.