Greenville is a city in and the county seat of Darke County, Ohio, United States. It is located near Ohio's western edge, about 33 miles (53 km) northwest of Dayton. The population was 12,786 at the 2020 census.

Darke County is a county in the U.S. state of Ohio. As of the 2020 census, the population was 51,881. Its county seat and largest city is Greenville. The county was created in 1809 and later organized in 1817. It is named for William Darke, an officer in the American Revolutionary War. Darke County comprises the Greenville, OH Micropolitan Statistical Area, which is also included in the Dayton-Springfield-Sidney, OH Combined Statistical Area.