Governor Pat Quinn has said he will sign the bill into law.
From the AP:
A historic vote Thursday in the Illinois House positioned that state to become the largest in the heartland to legalize gay marriage, following months of arduous lobbying efforts by both sides in President Barack Obama's home state.
Lawmakers voted 61-54 to send the measure back to the Senate to change the bill's effective date, just a technical change since the chamber already approved the measure in February. The measure will then head to Gov. Pat Quinn, who has pledged to sign it into the law.