The bill's sponsor, Sen. Heather Steans, D-Chicago, called it "a vote for the history books." She said the measure's strong showing in the Senate — where it needed 30 votes to pass — and the support of one Republican were good signs of what's to come.
Rep. Greg Harris, D-Chicago, said "the prospects are very good" in the House, though he declined to discuss the roll call so far or say when a hearing will be held. But other supporters said it could be within the next two weeks.
"As soon as we can send this bill to the governor and it becomes the law of the land I will be very happy person and so will tens of thousands of families across Illinois," Harris said.
Polls show voters' feelings shifting rapidly in favor of gay rights. President Barack Obama said last year he supports same-sex marriage, and in November voters in four states either approved or voted down bans on gay marriage.
Illinois wasn't the only state where supporters of legalizing gay marriage picked Valentine's Day to publicize their cause.
In Oregon, the state's leading gay-rights group formed a campaign organization to get a constitutional amendment on the November 2014 ballot. And in Minnesota, more than a thousand activists rallied at the state Capitol in support of legalizing gay marriage, just months after voters defeated a measure that would have banned it.
Opponents have said they're concerned the bill would force religious organizations to allow same-sex marriage ceremonies in their fellowship halls, parish centers, or even in their sanctuaries.