Glencar Lough lies in the Glencar Valley, between the Dartry Mountains to the north and the mountain range including Cope's Mountain to the south. The lake is located about northeast of Sligo and about west of Manorhamilton. It is long from west to east and wide. The lake has two crannogs (artificial islands): one at the western end near the Drumcliff River outlet and the other at the eastern end near the Diffreen River.