Allegheny County

Allegheny County is a large urban county in Pennsylvania, United States. As of the 2025 census estimate, the population was 1,225,035, a 2% decrease of 25,543 residents since 2020, making it the state's second-most populous county, after Philadelphia County. Its county seat and most populous city is Pittsburgh, Pennsylvania's second most populous city. The county is part of the Greater Pittsburgh region of the commonwealth, and is the center of the Pittsburgh media market.