Knox County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 62,721. Its county seat is Mount Vernon. The county is named for Henry Knox, an officer in the American Revolutionary War who was later the first Secretary of War. Knox County comprises the Mount Vernon, OH Micropolitan Statistical Area, which is also included in the Columbus-Marion-Zanesville, OH Combined Statistical Area.

Mount Vernon is a city in and the county seat of Knox County, Ohio, United States, along the Kokosing River. It is located 40 miles (64 km) northeast of Columbus. The population was 16,956 at the 2020 census.