In The Book of Ulster Surnames by Robert Bell (3) the nearest entry is:
Carlin (also Carolan)
Though these surnames were originally rendered in English O’Carolan itself was an Anglicisation of two entirely distinct Gaelic names. Carlin is the more usual form in the counties Tyrone and Derry, where it derives from O’Caireallain, the leading sept of Clann Diarmada. In Co Donegal the sept were erenaghs of the church lands of Clonleigh in the barony of Raphoe.
In Co. Cavan Carolan is more popular from the O’Cearbhallain sept who early migrated across the provincial border into Co Meath. Turlough O’Carolan, 1670-1738, the famous blind harper and composer, was of this sept.
Both these names were also anglicised as Carleton (see Carleton).
This connection with the Clann Diarmada comes up a few times and there is an inferred connection to the Ui Mhic Carthainn of whom they may have been chiefs.
3 The Book of Ulster Surnames by Robert Bell ISBN0-85640-602-