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 County makes up the Warren, Pennsylvania micropolitan statistical area. The county is part of the North Central Pennsylvania region of the state.