Warren County is a county located in the U.S. state of Pennsylvania. As of the 2010 census, the population was 41,815. Its county seat is Warren. Warren County was formed in 1800 from parts of Allegheny and Lycoming counties; attached to Crawford County until 1805 and then to Venango County until Warren was formally organized in 1819.
Warren County makes up the Warren, Pennsylvania Micropolitan Statistical Area.
Note: total for 1890 includes population (99) of Cornplanter Indian Reservation, reported separately.