Illinois Governor Pat Quinn signed a gun-control measure into law on Sunday that expands background checks to cover all firearms purchases in the state, closing what he said was a loophole that exempted gun sales between private parties.
The new law also requires all gun owners to report any lost or stolen firearms to local police within 72 hours.
"Guns are a plague on too many of our communities," Quinn, a Democrat, said in a statement. "Making sure guns do not fall into the wrong hands is critical to keeping the people of Illinois safe. This commonsense law will help our law enforcement crack down on crime and make our streets safer."
The expanded background checks go into effect on January 1, 2014.
Previously in Illinois, where Democrats control the state legislature but remain sharply divided over firearms safety, only adults buying guns from a licensed firearms dealer or at a gun show in the state have been subject to background checks.
Those buyers must have a firearm owners identification (FOID) card, which is issued by Illinois state police to applicants who pass a screening of state criminal and mental health records. The seller must then call a state-run hotline to check that a buyer's FOID card is valid before making the sale.
Under the new law, gun sales or transfers between private parties, including those that take place online, will have to follow the same system.
Not all of Quinn's gun-control efforts, which tend to draw greater support in the state's cities than in its rural areas, have been successful.
In July, state lawmakers voted to override the governor's veto of parts of a gun bill allowing individuals to carry more than one gun, to carry guns into some places that serve alcohol, and to carry a partly exposed gun.
The bill was drafted after a federal appeals court struck down the state's law banning people from carrying a concealed weapon in public last December, saying it violated the constitutional right to bear arms.
In April, the U.S. Senate rejected an effort, championed by President Barack Obama, to pass new federal gun-control laws, including an expansion of background checks to include people buying guns online or at gun shows.