Greenville is a city in Darke County, Ohio, United States. The population was 13,227 at the 2010 census. It is the county seat of Darke County.
Greenville is the historic location of Fort Greene Ville, a pioneer fort built under General Anthony Wayne's command. At over 55 acres (220,000 m2) this was the largest wooden fortification ever built. It was here that the Treaty of Greenville was signed on August 3, 1795, bringing peace to the area and opening up the Northwest Territory for settlement. Fort Greene Ville was named for Wayne's fellow General Nathanael Greene.
According to the United States Census Bureau, the city has a total area of 6.0 square miles (16 km2), all of it land.