Clark County is a county located in the west central portion of the U.S. state of Ohio. As of the 2020 census, the population was 136,001. Its county seat and largest city is Springfield. The county was created on March 1, 1818, and was named for General George Rogers Clark, a hero of the American Revolution.

Springfield is a city in and the county seat of Clark County, Ohio, United States. The municipality is located in southwestern Ohio and is situated on the Mad River, Buck Creek, and Beaver Creek, approximately 45 miles (72 km) west of Columbus and 25 miles (40 km) northeast of Dayton. As of the 2020 census, the city had a total population of 58,662, while the Springfield metropolitan area had a population of 136,001 residents.