Variant spellings include Drennen, Drenning, Drennon, Drinan, Drinnan, Drinnon, and Drynan.
[3] The Irish Uí Draighnáins, a descendant clan of the dynasty of Uí Maine, specifically claiming descent from the Síol Anmchadha branch,[4] were chiefs of the country lying around Sliabh Eisi, on the borders of County Clare and Galway.
They were formerly hereditary chief Brehons or judges of the principalities of Hy-Many and Hy-Fiachra Aidhne, in South Connacht, and had their chief residence at a place called Ard-na-Cno, in the parish of Killiny, and barony of Kiltartan, as we are informed in the Book of Lecan: "To the Aes Brengair belongs the stewardship of the arch-chief of Hy-Many, and it is the office of the Ui-Draighnen to distribute justice to the tribes.
In 1881 there were 404 people with the surname in Great Britain, primarily at Renfrewshire, Ayrshire, Lanarkshire, and Lancashire.
[1] The 2010 United States Census found 4,233 people with the surname Drennan, making it the 7,821st-most-common name in the country.