If you are working in Missouri for the next 3 to 12 months you are probably considered a resident of MO and will need to exchange your Illinois driver's license for a Missouri license. You will need to check with the MO Department of Revenue, Driver's License Department to find out for certain.

If you are considered a resident of MO, typically you will need to have the vehicle you drive on Missouri roads covered by Missouri insurance. Also, it is unlikely that your dad's insurance company will want to cover the vehicle that you are keeping in MO for this length of time since it will not be residing with your father in IL.

One reason for this is that Illinois and Missouri have different mandatory insurance requirements. Illinois requires 20/40/10 limits while MO requires 25/50/10 plus uninsured motorist bodily injury insurance of 25/50.

If you were the owner of the vehicle it would be easier to obtain insurance in Missouri because you would be able to title and register it in that state. To verify if it is legal to keep the car titled and registered in Illinois while the car is kept and insured out of state you will need to contact the IL Services for Drivers. If you are not able to do so, your dad might need to add you as a co-owner so that you can register the car in MO while you reside there.