Lewistown is an unincorporated community and census-designated place in central Washington Township, Logan County, Ohio, United States. As of the 2020 census, the population was 202. Until the 1829 Treaty of Lewistown, the community was the site of a Shawnee Native American reservation, also called Lewistown, named after Captain John Lewis, a Shawnee leader. Nearby Indian Lake was once known as the Lewistown Reservoir, after this settlement. It has a post office with the ZIP code 43333.