Richland County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 124,936. Its county seat is Mansfield. The county was created in 1808 and later organized in 1813. It is named for the fertile soil found there. Richland County is included in the Mansfield, OH Metropolitan Statistical Area as well as the Mansfield-Ashland-Bucyrus, OH Combined Statistical Area. The county is one of the six Metropolitan Statistical Areas that make up Northeast Ohio.