You will have to pay taxes on the car BUT, it depends on how each state collects it's taxes. Some states (i.e. Wisconsin) can not collect taxes for another state. So if an out of state resident buys a vehicle in WI, no taxes are involved, they are issued a temporary WI license plate good for 30 days, and they will receive a WI title (WI is NOT a title holding state like Colorado). When they get the WI title, they go to the DMV of the state that they live in and pay their local taxes on the cash selling price of the vehicle and at that time the vehicle will be registered to that state. You will, however, ALWAYS pay taxes for where you live. If MO can collect taxes for IL, then you will pay IL taxes. If you are buying from a dealership, ask to speak with the finance manager to find out how IL deals with situations like that. If you are leasing a vehicle from another state, this is a totally different process because taxes are figured only on your payments in a lease and if you lease a vehicle, 95% of the time the leesor or leasing institution will keep the title.