Harris recently announced that he was considering moving the bill, which would overturn the state's ban on same-sex marriage, during the General Assembly's lame-duck session.

On Dec. 13, he announced that the time was right.

Same-sex marriage advocates believe outgoing lawmakers could be more likely to vote on the measure without fear of voter reprisal. Sweeping victories for LGBT candidates and Democrats across the country this November enthused marriage equality proponents in Illinois. Harris had previously stated that his calling the bill to a vote could depend on November election results.

Those wins significantly sped-up efforts to pass same-sex marriage legislation in Illinois, said Randy Hannig, public policy director for Equality Illinois.

"If you would have asked me a year ago… I would have said give [marriage legislation] a couple of years," Hannig said.

Supporters of the bill already have the backing of Gov. Pat Quinn and Chicago Mayor Rahm Emanuel.

Civil unions have been available in Illinois since June 2011, but many couples believe that they fall short marriage equality. Couples have reported problems at hospitals and employers. Last December, Springfield's city government initially voted not to extend its self-funded health benefits to civil union couples.

Citing those shortcomings, the American Civil Liberties Union of Illinois and Lambda Legal filed coordinated lawsuits against Cook County Clerk David Orr, that seek to overturn the state's ban on same-sex marriage. Orr has refused to fight the lawsuits, which have been taken up by downstate clerks.

The combination of both the lawsuits and momentum around the marriage bill, have made many in the nation eye Illinois as the next probable state to win marriage equality.

Rep. Kelly Cassidy, a sponsor of the HB 5170, encouraged LGBT people and their allies to talk to their state lawmakers about why marriage equality matters, especially if those lawmakers represent districts outside of Chicago.

"When we tell [lawmakers] that their districts have changed, we really need to show them that they have," Cassidy said. "We need to get our butts off the Lakefront, frankly."

Rick Garcia, director of The Civil Rights Agenda's marriage project, warned that significant work remains before the bill can be called to a vote.

"Those last handful of votes that carry you to victory, it's like herding calves," he said. "Serious hard work still needs to be done."

Garcia urged LGBT supporters to call their lawmakers and ask friends and family to do the same.

Harris and others have cautioned that they will not call the bill until they are confident they have the votes to pass it, as doing so prematurely could lock lawmakers into "no" votes.

But, Cassidy said, the momentum is there to pass the bill.

"It is absolutely possible," she said.