In the 1901 Irish Census, 14,673 people are recorded with the surname Brennan (with this exact spelling) on the island of Ireland. So if your name is Brennan and you are searching for an Irish ancestor with the name Brennan, you will work hard in your search!
In alphabetical order by county;
King's County 958
Queen's County 958
Unsurprisingly, Kilkenny has the largest number of people with the Brennan name (1,932), Dublin is next and Sligo, Roscommon and Mayo follow close behind.
In addition there are
146 people recorded with the name Brenan (exact spelling),
I'm a Brennan with clear roots in Clawinch Island, Co. Longford (on the Shannon) Brennan Family Clawinch, Co. Longford and possibly in Kilteevan, Co. Roscommon. As a child my father's people told me that our family came from Kilkenny originally and that Cromwell threw us out. This story has intrigued me all my life and of late I have begun to collect information about Brennans the world over. If you have Brennans in your family, you are cordially invited to join me and maybe we will get to the root of this family story, or maybe not...