Ohio State Route 122 runs easterly, then southeasterly, then easterly again, in western Ohio. It's best known in the areas Eaton and Middletown, as it serves both of these towns. Ohio Route 122 begins at the Indiana state line, southeast of Richmond, Indiana. (The continuation of the road toward the west doesn't carry any numbered designation.) From there, Ohio Route 122 heads due east to Eaton. At the central junction of Eaton, Ohio Route 122 carries US Route 35 easterly for a bit, crossing US Route 127, which carries Ohio Route 732's northernmost piece toward the south. Soon, Ohio Route 122 continues southeasterly, leaving US Route 35 to continue as the easterly route. This is the start of Ohio Route 122's southeasterly portion, which meets Ohio Route 725 at Gratis. Once it enters Butler County, it meets the eastern end Ohio Route 744, where Ohio Route 122 takes over as the easterly route into Middletown. In Middletown, Ohio Route 122 uses the farthest-separated pair of one-way streets I've ever seen used by a single route designation. Ohio Route 122 continues east to a point just north of Lebanon, where it ends at Ohio Route 48.