Dunegan is a variant of the Irish surname, Ó Donnagáin. A more common spelling is Donegan.
It was first found in the County Cork where they were anciently seated at Muskerry, later moving to Limerick, Kildare, and Dublin.
One of the first settlers with this name or its variants were: Thomas Donegan, the Earl of Limerick, who became Governor of New York from 1683 until 1691.
It is also the name of a townland in Ballyloughloe civil parish, barony of Clonlonan, County Westmeath.