GILPIN: 1. English: In the northeast, from the Gilpin river in Cumbria; in southern counties, probably a variant of Galpin. 2. Irish (Connacht): Reduced Anglicised form of Gaelic Mac Giolla Fionn "son of the fair-haired lad". In Ulster, the name may be of northern English origin (see 1 above).
GALPIN: 1. English: Occupational name for a messenger or scullion (in a monastery), from Old French galopin "page"/"turnspit", in turn from galoper "to gallop".
I included Galpin for the sake of completeness only. Obviously, you're interested in the Irish derivation.