It's still not clear if the bill will be called for a vote. The bill passed the Senate in February, but the sponsor delayed the House vote in May. He said he would wait to call it until he has enough votes to pass it.
Still, those for and against the bill are planning to rally next week anyway.
"The trend recently has been in favor of redefining marriage, but there are still a majority of states in the country that haven't done it. The Supreme Court in its decisions in June said this was the privy of the state, so we have every right to keep marriage as it's always been and we hope that we will," said Zachary Wichmann of the Catholic Conference of Illinois.
Supporters of the bill say they simply want marriage equality for all.
If passed, Governor Pat Quinn says he will sign the bill into law.