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Chapter 625 ILCS 5/3-804(b)
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For the Illinois guys, straight from the State of Illinois General Assembly's web site....
http://www.ilga.gov/legislation/ilcs/ilc...Vehicle+Code%2E
(b) Any person who is the registered owner of an antique vehicle may display a historical license plate from or representing the model year of the vehicle, furnished by such person, in lieu of the current and valid Illinois antique vehicle plates issued thereto, provided that valid and current Illinois antique vehicle plates and registration card issued to such antique vehicle are simultaneously carried within such vehicle and are available for inspection.
(Source: P.A. 91‑37, eff. 7‑1‑99.)