More information is needed.
First, are you a resident of Missouri or Illinois (or someplace else)? What’s your resident/non-resident/part-year resident status of each? It’s important that you enter your non-resident state information before your resident state data, or errors can ensue. See the TurboTax Help article How do I file a nonresident state return? for more information.
Next, what is the “incorrect state tax” that’s being pulled in? What appears to be wrong, and why do you think it’s wrong? What is your tax on line 30 of Form MO-1040? What is your Missouri taxable income on line 29? What is your filing status – married filing combined or married filing separately?
Any other information you might provide would be helpful.
