Patriot is correct about taking 79 once you get to the O'fallon or Troy area.  Used to have some good friends who lived around there so know those backroads pretty well.  Last summer Megan and I stayed at a bed & breakfast in Hannibal one night on a trip to STL, had a great time and drove down 79 leaving town it is exactly what you're looking for.  And for the other end, you really can't go wrong staying in LeClaire.  Awesome views, awesome food, a distillery and microbrew and great shops all in easy walking distance.   I'm going to Bookface message you some links to places you might want to check out.