Dont believe anything was passed at the state level in IL. IL law specifically calls out permission to sell longguns to contiguous states iirc.
I would assume a WM policy change but something more regional since out of staters are buying firearms (non IL/MO states) in the WM deals thread.
(430 ILCS 65/3a) (from Ch. 38, par. 83-3a)
Sec. 3a. (a) Any resident of Illinois who has obtained a firearm owner's identification card pursuant to this Act and who is not otherwise prohibited from obtaining, possessing or using a firearm may purchase or obtain a rifle or shotgun or ammunition for a rifle or shotgun in Iowa, Missouri, Indiana, Wisconsin or Kentucky.
(b) Any resident of Iowa, Missouri, Indiana, Wisconsin or Kentucky or a non-resident with a valid non-resident hunting license, who is 18 years of age or older and who is not prohibited by the laws of Illinois, the state of his domicile, or the United States from obtaining, possessing or using a firearm, may purchase or obtain a rifle, shotgun or ammunition for a rifle or shotgun in Illinois.