When an Illinois resident purchases a car from an out-of-state dealer and will title the car in Illinois, the sale and subsequent tax due is reported on Form RUT-25 when you bring the vehicle into Illinois. You should attach a copy of the bill of sale as proof of the purchase price. For information about reporting the tax due, see Form RUT-25 instructions, Publication STS-76, Illinois Vehicle Tax Guide, or 86 Ill. Adm. Code 150.705.