Longford is an inland county of Ireland in Leinster Province Province, bounded on the northeast by County Cavan, on the east and south by Westmeath, on the west by Roscommon, and on the northwest by County Antrim. Its area is 421 square miles.
The only heights of the county are along the Roscommon and Leitrim border. The River Shannon forms the western border, expanding southwest into Ree Lough. Other rivers are the Inny, Black, and Camlin. The Royal Canal crosses the southern half of the county, connecting the Shannon with the city of Dublin by way of Mullingar. Lakes in Longford include Gowna, Forbes, Derrylough, Ree, Kinale, and Bannow.
Longford, which has a notable 19th-century cathedral, is the county seat. Other important towns are Granard, Ardagh, Keenagh, and Edgeworthstown. There are noteworth monastic remains on the islands in Ree Lough.