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 largest city is Pittsburgh, Pennsylvania's second largest city. The county is part of the Greater Pittsburgh region of the commonwealth, and is the center of the Pittsburgh media market.
- Country
- United States
- Headquarters
- Pittsburgh City-County Building
- Inception
- September 24, 1788
- Website
- http://www.county.allegheny.pa.us/, https://www.alleghenycounty.us/Home
