Jefferson County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 65,249. Its county seat is Steubenville. The county is named for Thomas Jefferson, who was vice president at the time of its creation. Jefferson County is part of the Weirton–Steubenville, WV–OH Metropolitan Statistical Area, which is also included in the Pittsburgh–New Castle–Weirton, PA–WV–OH Combined Statistical Area.