Offaly is an inland county of central Ireland in Leinster Province
. It is bounded on the north by County Meath
, on the east by County Kildare
, on the south by County Laois
and County Tipperary
, and on the west by Roscommon
and County Galway
. It has an area of 770 square miles.
The surface of the county is occupied by a high plain and in the northeastern part, the Bog of Allen. The county's only mountains, the Slieve Bloom Hills, with summits reaching 1500 feet, extend along the south central boundary. The northernmost tip of Lake Derg lies at the southwestern edge of the county. On the northwest, the River Shannon forms part of the boundary. Most of the northern plain is drained by the Brosna and Clodia. In the east are the rivers Boyne, Barrow, and Figili. The Grand Canal, connecting the Shannon with the Liffey, crosses the county east to west.
Tullamore, the county seat, is the most important town of the district. Birr, Portarlington, and Philipstown are market centers.