Clermont County, popularly called Clermont, is a county in the U.S. state of Ohio. As of the 2020 census, the population was 208,601. Ordinanced in 1800 as part of the Virginia Military District, Clermont is Ohio's eighth oldest county, the furthest county west in Appalachian Ohio, and the eleventh oldest county of the former Northwest Territory. Clermont County is part of the Cincinnati, OH-KY-IN Metropolitan Statistical Area. The county is named from the French "clear hills or mountain."