can't help. have no experience bike riding between st. louis and cincinnatti. but there are plenty of online map routing sites.
southern indiana, from personal experience motorcyling across it a number of times, should be a piece of cake to find a few lonely, out of the way roads, and same for illinois. you might want to start with how and where you plan on crossing the mississippi. i usually try to find a ferry, if i can. they still run them across the mississippi in places.