The Castletown River (Irish: Abhainn Bhaile an Chaisleáin) is a river which flows through the town of Dundalk, County Louth, Ireland. It rises near Newtownhamilton, County Armagh, Northern Ireland, and is known as the Creggan River in its upper reaches. Its two main tributaries are the and rivers and it enters the Irish Sea at Dundalk Bay.