Lancaster is a city in Fairfield County, Ohio, and its county seat. The population was 40,552 at the 2020 United States census, making it Ohio's 30th largest city, having surpassed Warren and Findlay due to its own growth while the latter two cities declined. The city is near the Hocking River in the south-central part of the state, about 33 miles (53 km) southeast of Columbus and 38 miles (61 km) southwest of Zanesville. It is part of the Columbus metropolitan area.