Rathvilly (Irish: Ráth Bhile[1]) is a barony in County Carlow, Ireland.

Rathvilly barony takes its name from the village of Rathvilly, which derive from the Irish language Ráth Bhile, meaning "rath of the sacred tree".

Rathvilly barony is bordered by the following baronies: to the west by Carlow; to the south by Forth; to the north by Upper Talbotstown; to the east by Ballinacor South; to the southeast by Shillelagh; and to the northwest by Kilkea and Moone.

In the 5th century, Crimthan, King of Leinster, lived at Rathvilly.

The territory was that of the Uí Felmelda Tuaid, a Uí Cheinnselaig sept descended from Feidlimidh son of Enna Ceansalagh and brother of Crimthan.