I would recommend riding theKaty Trail to cross Missouri for several reasons. A prime one is to avoid the never-ending short, steep hills that cover most of the state; surveys of some TransAm riders have rated Missouri as the toughest part of the route. Also I found the Katy scenic, and and it's relaxing -- not having to deal with traffic and being able to communicate easily with other trail users. The trail can get somewhat soft after rains and, when dry, will leave your bike dusty, but it's a great ride. What ever way you get to the St. Louis area, you might want to take the Great River Road along the Mississippi north from there to about mid-Illinois, then head to your destination. Southern Illinois is also very hilly.