The Finn River (Irish: An Fhinn or Abhainn na Finne), also known as the River Finn, is a small river that flows through parts of County Fermanagh and parts of County Monaghan in the south of Ulster, the northern province in Ireland. In certain places, the river forms part of the boundary between County Fermanagh, which is part of Northern Ireland, and County Monaghan, which is part of the Republic of Ireland. Two very short stretches of the river, just north of Redhills and at Castle Saunderson, near Belturbet, also form part of the boundary between County Fermanagh and County Cavan (part of the Republic of Ireland). This means that some stretches of the river form part of the border between Northern Ireland and the Republic of Ireland, these short stretches also forming part of the extern