Lancaster is a city in Fairfield County, Ohio, United States. As of the 2010 census, the city population was 38,780. It is located near the Hocking River, approximately 33 miles (53 km) southeast of Columbus, Ohio. It is the county seat of Fairfield County. The current mayor of Lancaster is Republican David S. Smith, who took office in January 2004. In November 2007, Smith won reelection to a second four-year term commencing in January 2008.