Chillicothe )is a city in the U.S. state of Ohio and the county seat of Ross County,(;.Chillicothe was the first and third capital of Ohio and is located in southern Ohio along the Scioto River. The name comes from the Shawnee name Chalahgawtha, meaning "principal town", as it was a major settlement of that people. They and their ancestors inhabited the territory for thousands of years prior to European contact. At the time of European-American settlement, the community was plotted by General Nathaniel Massie on his land grant.The population was 21,797 at the 2000 census. According to the U.S. Census Bureau's annual estimates, Chillicothe had a population of 22,296 in 2008, while the Columbus-Marion-Chillicothe, OH Combined Statistical Area has 2,002,604 people. It is the only city in Ross County and the center of the Chillicothe Micropolitan Statistical Area (as defined by the United States Census Bureau in 2003).Chillicothe is a designated Tree City USA by the National Arbor Day Foundation.