About Irish Surnames

It is very common in English-speaking countries to have surnames based on the Christian name of the father. For example, the Irish “O”, as in O’Duffy, means the grandson of Duffy. In England, “Fitz” is used to indicate illegitimacy (i.e. Fitzpatrick, Fitzmichael). In Scotland and Ireland, “Mc” or “Mac” means “the son of” , i.e. McDuffy, MacDuffy.

“Son” that is added on the first name such as Jameson, Thomason and Michaelson literally means the son of James, Thomas and Michael. (Grandma Sarah, birth name Sigrid, married Grandpa Paul Hanson.) Norwegian / Danish addition of "sen" is similarly expressed, in Hansen. This is the patrynomic naming system. Sometimes, adding “s” to the first name like that of “Williams”, "Patricks", and “Michaels” is also used.