Lewistown is a census-designated place in central Washington Township, Logan County, Ohio, United States. Until the 1829 Treaty of Lewistown, the community was the site of a Shawnee settlement. It is said to have been named in honor of “Captain” John Lewis, a Shawnee leader. Nearby Indian Lake was once known as the Lewistown Reservoir, after this settlement. Although it is unincorporated, it has a post office, with the ZIP code of 43333. The population of the ZCTA for ZIP code 43333 was 693 at the 2000 census.