Recorded as O' Tolan, O' Twolan, Tolan, Toland, Toolan, Toolin, apparently Thulis, possibly on some occasions O' Toole, and probably others, this is an ancient Irish surname of very confusing origins. It is or was originally a County Donegal name, although in the 17th century much of the sept moved down to County Mayo where they "lost" the O' prefix. The meaning of the name is unclear, but it seems to derive from the pre 13th century Gaelic O' Tuathalain suggesting that it was probably religious and may translate as "The male descendant of the follower of the lord". Many Irish surnames do have a holy or religious origin, and this could well be one of them. It is also claimed that the clan were fighting men, being followers of the O'Donnells, when they lead their abortive rebellion against English rule in 1602. However the famous Irish etymologist, the late Edward Lysaght also showed that the clan were to be found in County Sligo, with a Petrus O' Tuathalain being the vicar of Killaspugbrone in the barony of Carbury, in the year 1306. This is about as ancient as a surname gets.