Marathon is an unincorporated community and Census-designated place in northeastern Jackson Township, Clermont County, Ohio, United States.[1] Although it is unincorporated, it had a post office, with the ZIP code 45145.[2] The current ZIP code is 45118.[3] It lies along U.S. Route 50.
Marathon was originally called Cynthiana, and under the latter name was laid out in 1838.[4] A post office called Marathon was established in 1845,[5] and remained in operation until it was discontinued in 2011.[6]