Quick answer: complete the Small Estate Affidavit describing the vehicle, attach a death certificate and (if there's a will) a certified copy, surrender the title, and submit everything to the Secretary of State's Vehicle Services Department with a $3 title fee.
No value ceiling when used just for the car
What the Secretary of State needs
Illinois Administrative Code Title 92, Section 1010.150 lists the requirements: the Small Estate Affidavit describing the vehicle by model year, make, and VIN; a copy of the death certificate for deaths on or after September 16, 1985; a certified copy of the will if the owner died testate; the decedent's original title, surrendered; and a completed, signed application for title from the transferee.
A modest, specific fee
The transfer itself costs a $3 title fee, plus any applicable registration fees and proof of compliance with, or exemption from, Illinois's Vehicle Use Tax.
Where it's submitted
Documents go to the Vehicle Services Department within the Office of the Secretary of State — either in person at a facility or by mail to the Department's Springfield office, with payment for the fees and taxes included.
Joint title skips this process entirely
If the title was held jointly by the decedent and another person, a different, simpler procedure applies instead of the Small Estate Affidavit route.
A local probate attorney can review your estate — many offer a free consultation.
The Secretary of State processes this the same way regardless of which Illinois county the vehicle was registered in.