Caisleán na Finne, meaning "castle of the (river) Finn"), sometimes spelt Castlefinn, is a market town in the Finn Valley of County Donegal, Ireland.
The town has a population of 810 (2006) and is located between Ballybofey and Lifford. The River Finn flows by the town. The town is located in along the main N15 national primary road, which runs from Bundoran to Lifford.
The town lies 6 miles from Lifford and 8 miles from the twin towns of Ballybofey /Stranorlar. It has close links to the twin towns of Ballybofey/ Stranorlar, Letterkenny and has strong links with West Tyrone in Northern Ireland, especially with the towns of Strabane and Castlederg.