Donegan Surname in Ireland This varies, but Donegan is thought to be the most common form. My father and his family always spelled their name 'Dunican', and other forms include Doonican and Dunnegan. I have never seen it with an 'O' prefix. We emanate mainly from around the Blackwater river valley in Cork, and Louth, and in Westmeath, where I live, there is a townland of Dunegan, often cited as the original place of settlement of the Donegan clan in the Midlands. I hope this piece of trivia has been informative.