State Route 122 (SR 122) is an Ohio state highway which runs from the Ohio-Indiana state line in Preble County east of Eaton, Ohio to SR 48 near Lebanon, Ohio, a distance of 43.4 miles (69.8 km). When the route was designated in 1923, it ran along its current route from Indiana to Middletown. It was extended to its current eastern terminus in 1937 but was extended further east to U.S. Route 42 in 1946.