Árainn Mhór is an island off the west coast of County Donegal in Ulster, Ireland. Arranmore is the largest inhabited island of County Donegal, with a population of 514 in 2011, down from 528 in 2006, 543 in 2002, and over 600 in 1996. The island is part of the Donegal Gaeltacht, with most of the inhabitants speaking Ulster Irish.