revealed spelling variations , including Brennan, McBrennan, Brannon, Brannan, Brannen, Brannin, Brennyn, Brannyn, MacBrennan, Brenan, Branon, Branan, Branen and many more. First found in County Kilkenny , where they held a family seat from very ancient times, long before the Norman Conquest in 1066.   More More about the O'Brennan History...