The Storm Prediction Center has issued Severe Thunderstorm Watch #430 for parts of eastern Missouri (including southeast Missouri) and southwestern Illinois. The watch is in effect until 6:00am CT Tuesday.
A large complex of storms is moving east across the state of Missouri. You can see in the above image that the entire line is already starting to bow. The main threat from the line that is moving east will be damaging winds.
I think the storms will start to move in the the "Heartland Counties" around 3:00am'ish.
Storms are expected to move east at 45mph.