OConnor is the most illustrious of all Irish names. There are six distinct septs of the name. The first are the OConnors of Connacht-the main branches being OConor Don, OConor Roe and OConor Sligo. They are descended from Conchobhar, King of Connacht (d.970) and claim the last two Kings of Ireland, Turlough OConnor(1088-1156) and Roderick OConnor (1116-1198). Their direct descendant is the present OConnor Don: Denis OConnor. It should be noted that this important family consistently maintained its position AND remained inflexibly Catholic.
The O'Connor Kerry derive their name from a different Conchobhar who was Lord of an extensive area of Northern Kerry, but after the Anglo-Norman invasion of 1170, they were pushed northward toward Shannon. The OConnor Kerry sept is the most numerous sept. Estimates put the number of this sept in Ireland today at 30, 000. Some members of this sept changed their name to Conner.
The OConnors of Corcomroe, a barony in North Clare, are descended from Conchbhar, lord of Corcomroe (d. 1002)
The OConnors of Offlay are descended from OConnor Faly, who in turn was descended of Cathaoir Mor, King of Ireland in the second century.
The OConnor in Keenaght (Derry) were once very powerful. In the twelfth century they were overpowered by the O'Kanes. Families of these OConnors are still found in that part of Ulster.
The OConnors of Glengiven were of royal blood, their ancestor being Cian, son of Oilioll Olum, King of Munster in the third century.