CASLIN Family History
Recorded as Caslan, Caslin, Caslane, Caslyn, Casillan, but in former times befoe the 17th century as O' Caisealain, this is an Irish surname. It is said to be almost exclusively from the county of Roscommon, and the best explanation we can offer for the meaning is that it is topographical. If so it described either a person who lived by a caislean (castle) or by a caislin, a small stream. The literal meaning is probably "The male descendant of the person who lived by a castle (or small stream)" but given the variation in Gaelic interpretations, no doubt other explanations are possible.