Old Fort is a census-designated place located in northern Pleasant Township, Seneca County, Ohio, United States. Although it is unincorporated, it has a post office, with the ZIP code of 44861.
Old Fort was platted in 1882, and named after Fort Seneca, a fort built during the War of 1812. A post office has been in operation at Old Fort since 1882.
Old Fort High School is located on County Road 51.