county, northwestern Pennsylvania, U.S., consisting of a hilly region on the Allegheny Plateau that is located midway between the cities of Erie and Pittsburgh and is bisected by the Allegheny River.

Venango county was formed in 1800; its name was derived from an Iroquoian Indian word probably meaning “bull thistle.” In August 1859 Edwin L. Drake (Drake, Edwin Laurentine) triggered Pennsylvania's oil boom when he drilled the nation's first successful commercial oil well along Oil Creek in present-day Oil Creek State Park. The county developed further when oil was discovered in Franklin (the county seat) in 1860 and when natural gas was found in the township of Pine Grove in 1885. Oil City became a major shipping point for crude oil in the late 19th century.

The main components of the economy now are services, manufacturing, and coal mining. Area 675 square miles (1,749 square km). Pop. (2000) 57,565; (2007 est.) 54,763.