Warren County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 38,587. Its county seat is Warren. The county was established in 1800 from parts of Allegheny and Lycoming counties; attached to Crawford County until 1805 and then to Venango County until Warren was formally established in 1819.

Warren is a city in and the county seat of Warren County, Pennsylvania, United States, located along the Allegheny River. The population was 9,404 at the 2020 census. It is home to the headquarters of the Allegheny National Forest and the Cornplanter State Forest. It is also the headquarters for the Chief Cornplanter Council, the oldest continuously chartered Boy Scouts of America Council, and the catalog company Blair. Warren is the principal city of the Warren micropolitan area.