SR 121 was commissioned in 1931 routed between Richmond and the Ohio state line. In 1932 a second segment was added to the state road system routed between US 52 and Connersville.
SR 121 was a route established in 1931, running from Richmond to the Ohio state line. In 1932, an additional section of this road system was added, extending from US 52 to Connersville.