county, north-central Pennsylvania, U.S., constituting a mountainous upland region largely on the Allegheny Plateau. Notable features include Bald Eagle Mountain in the southwest and Pine Creek Gorge in the west. The county is drained by the West Branch Susquehanna River and Pine, Little Pine, Lycoming, Loyalsock, Muncy, and Little Muncy creeks. Recreational lands include Tiadaghton State Forest and Little Pine, Upper Pine Bottom, and Susquehanna state parks.

Lycoming county was created in 1795; its name was derived from a Delaware Indian word meaning “gravelly or sandy creek.” Williamsport, the county seat, was a major centre for lumbering in the 1860s. The city is the home of the Little League Baseball International Headquarters (Little League) (founded 1939) and the site of its annual World Series. The principal boroughs are South Williamsport, Montoursville, Jersey Shore, Muncy, and Hughesville.

A diversified manufacturing base includes many industries associated with lumbering and wood and paper products. Lycoming has the largest area of any county in Pennsylvania. Area 1,235 square miles (3,198 square km). Pop. (2000) 120,044; (2007 est.) 116,811.