Illinois gun owners will have to report missing firearms to police and check the background of potential buyers under a law Gov. Pat Quinn enacted Sunday.

Quinn signed the legislation at a South Side park near where an off-duty Chicago police officer was killed with an illegally trafficked gun in 2010. He said the law will make it easier to recover stolen weapons and help ensure that only responsible people buy firearms. The measure passed both chambers of the Illinois General Assembly with healthy majorities.
Illinois gun law signed Sunday requires gun owners to report missing firearms, check background of buyer - chicagotribune.com

And here's the actual bill: Proposed Illinois Gun Law HB1189 - American Gun Owners Alliance