Illinois drivers are generally required to register their vehicles and obtain insurance before driving on the road. At the time of registration, Illinois drivers receive license plates as evidence of registration and as a way for law enforcement officers to keep track of vehicles on the state's roads. Where you bought your car will determine how long you can drive without plates.
If you buy a vehicle from a licensed dealer in Illinois, he will likely take care of transferring the title and will issue you a temporary registration permit. You must display the temporary registration, which is good for 90 days, in place of the license plate on the back of your car. It is legal to drive without license plates as long as your temporary registration permit is valid and properly displayed. But you must obtain new license plates before the permit expires; alternatively, you can have the secretary of state's office reissue your temporary permit if you cannot obtain your license plates by the expiration date.
If you buy your vehicle from a private party without the assistance of a dealer, you can legally drive the vehicle without a license plate for 24 hours, but you must have the title to the vehicle with you when you are driving. Technically, you are only allowed to drive in the 24-hour period to get to an agent or secretary of state facility to get a temporary permit issued. If you choose to apply for title by mail, you can legally operate the vehicle without a temporary permit only if you have your title application, Form VSD 190, displayed in the lower right corner of your vehicle's front windshield. You put your signature on the application; state that the application being displayed is a copy and the original was mailed to the secretary of state's office; and state the date on which it was mailed.
It is unlikely a dealer will let you purchase a vehicle with someone else's license plates on it because most dealers remove old license plates before the vehicle goes up for sale. However, private parties sometimes leave license plates on a purchased vehicle. In Illinois, it is illegal to operate a vehicle with someone else's license plates. The plates belong to the vehicle's owner rather than to the vehicle itself. Thus, when you sell a vehicle you must remove the plates, and when you buy a vehicle you must remove the previous owner's plates.
To register your vehicle in Illinois, you must complete an Application for Vehicle Transactions, form VSD 190. You can complete the application online via the secretary of state's electronic system, but you must print the application and take it to the nearest secretary of state facility within seven days. Alternatively, you can obtain the application by visiting the facility in person. When you submit your application and paperwork, you must provide proof that you paid taxes on the vehicle.