Donegal County is part of Ulster Province, bounded on the west and north by the Atlantic, east by Lough Foyle, County Londonderry, and Tyrone, and on the south by County Fermanagh, Leitrim, and Donegal Bay. The area covered is 1862 square miles.
The coast is indented by numerous arms of the sea. The largest are Lough Swilly, Sheep Haven, Ballyness, and Gweebarra bays. Between loughs Foyle and Swilly is the large roughly rectangular peninsula of Inishowen, with Malin Head being the most northerly point on the island.
Lifford is the county seat. Letterkenny, Ballyshannon, and Buncrana are manufacturing towns.
There are numerous antiquities including round towers, stone crosses, an ancient hill fortress of North Irish kings, and the ruins of a 17th Jacobean castle.