Ross County is a county in the Appalachian region of the U.S. state of Ohio. As of the 2020 United States Census, the population was 77,093. Its county seat is Chillicothe, the first and third capital of Ohio. Established on August 20, 1798, the county is named for Federalist Senator James Ross of Pennsylvania. Ross County comprises the Chillicothe, OH Micropolitan Statistical Area, which is also included in the Columbus-Marion-Zanesville, OH Combined Statistical Area.

Chillicothe is a city in and the county seat of Ross County, Ohio, United States. Located along the Scioto River 45 miles (72 km) south of Columbus, Chillicothe was the first and third capital of Ohio. It is the only city in Ross County and is the center of the Chillicothe micropolitan area. The population was 22,059 at the 2020 census. Chillicothe is a designated Tree City USA by the National Arbor Day Foundation.