<Li> Lord of Dunkerron </Li> <Tr> <Th> Cadet branches </Th> <Td> O'Sullivan Mór O'Sullivan Beare O'Sullivan MacCragh MacCrohan McGillycuddy </Td> </Tr> <P> O'Sullivan (Irish: Ó Súilleabháin), also known as simply Sullivan, is an Irish Gaelic clan based most prominently in what is today County Cork and County Kerry . The surname is associated with the southwestern part of Ireland and was originally found in County Tipperary before the Anglo - Norman invasion . It is the third most numerous surname in Ireland . Due to emigration, it is also common in Australia, North America, Britain and the rest of the world . </P> <P> The O'Sullivans according to traditional genealogy were descended from the ancient Eóganacht Chaisil sept of Cenél Fíngin, the founder of the clan being placed in the 9th century, eight generations removed from Fíngen mac Áedo Duib, king of Cashel or Munster from 601 to 618 . Later they became the chief princes underneath their close kinsmen the MacCarthy dynasty in the small but powerful Kingdom of Desmond, successor of Cashel / Munster . The last independent ruler of the clan was Donal Cam O'Sullivan Beare, defeated in the Nine Years' War of 1594--1603 . </P>

Where did the last name sullivan come from