In signing the bill, Gov. Pat Quinn said the law is "going to help all of us be safe," the Chicago Tribune reported Monday.
Quinn signed the bill Sunday in a ceremony at a park on the South Side of Chicago near where an off-duty police officer was killed by an illegally trafficked gun in 2010.
Gun owners will now have to report stolen guns to police within 72 hours of the theft. Starting Jan. 1, private gun owners will have to contact Illinois State Police before selling or transferring a weapon to ensure the prospective buyer can legally possess a gun.
State Police Director Hiram Grau said he expected a verification system to be ready by January.
Addressing whether the law would push illegal buyers into other states that don't have such restrictions, Quinn said it was "really important" to have federal legislation, "but you've got to start somewhere."