Clarion County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 37,241. Its county seat is Clarion. The county was formed on March 11, 1839, from parts of Venango and Armstrong counties. Clarion County is entirely defined as part of the Pittsburgh media market. The county is part of the North Central Pennsylvania region of the state.

Clarion is a borough in and the county seat of Clarion County, Pennsylvania, United States. It is located 77 miles (124 km) north-northeast of Pittsburgh and is part of the Pittsburgh DMA. Clarion was settled in 1839 and incorporated in 1841. In the past, the surrounding area produced natural gas, oil, lumber and coal. The population was 2,004 in 1900, 2,864 in 1910, and 3,931 at the 2020 census, down from 5,276 at the 2010 census. It is home to the annual Autumn Leaf Festival and PennWest Clarion. The county courthouse was added to the National Register of Historic Places in 1979. Clarion County's designated tourism agency is the Clarion County Economic Development Corporation.