The festivities at the University of Illinois at Chicago featured a family-friendly crowd, musical performances and a stage lined with American, Illinois and rainbow flags.
"We understand in our state that part of our unfinished business is to help other states in the United States of America achieve marriage equality," Quinn said before he signed the bill on a desk once used by President Abraham Lincoln. He said part of that mission was to ensure that "love is not relegated to a second class status to any citizen in our country."
References to freedom, equality, fairness and Lincoln - the desk was where he penned his 1861 inaugural address - were peppered throughout the event. In attendance were top elected officials, including Illinois Attorney General Lisa Madigan and Chicago Mayor Rahm Emanuel. Organizers estimated roughly 2,300 attended, including activists and members of the public.
Illinois, where Democrats lead both legislative chambers and the governor's office, legalized civil unions in 2011, but the road to same-sex marriage was bumpy.
When 2013 began advocates hoped Illinois would've been the 10th state, but watched as other states passed it. Gay marriage is allowed in Washington D.C., and 15 other states; Hawaii's governor signed a measure last week.
Even with support from top business leaders, unions and some Republicans, several lawmakers were resistant to the idea. That included some Democrats in more conservative downstate Illinois and some Chicago-area lawmakers.
The measure was fought hard by some of the state's most well-recognized religious figures, including Cardinal Francis George of the Archdiocese of Chicago and the Rev. James Meeks, a former state senator who runs a politically-influential mega church in Chicago. Meeks was part of a coalition of black pastors who said marriage should remain between a man and woman and sponsored robocalls in several legislative districts and on the airwaves. The opposition placed black lawmakers in the House in a spotlight and several evaded public inquiries on the matter for months.
Although Illinois once appeared poised to become the first Midwestern state to approve gay marriage in the Legislature, Minnesota did it sooner and started holding its first same-sex weddings over the summer. Iowa allows gay marriages too because of a court ruling, not a legislative vote.
The Illinois Senate approved the measure on Valentine's Day, but the bill's main sponsor, Democratic state Rep. Greg Harris of Chicago decided against calling it for a vote in the House because he said he didn't have the needed support. In a tearful speech in front of his colleagues, he vowed to bring the measure back.
Proponents then launched another aggressive campaign with help from labor, the former head of the Illinois Republican Party and the ACLU. They billed the measure as a matter of civil rights and equality for families. Quinn and House Speaker Michael Madigan also persuade lawmakers in the final days.
The measure passed the Illinois House earlier this month by a narrow margin 61-54; It needed 60 votes to pass. But none of the opposition or slim margin was evident Wednesday at the event where the Chicago Gay Men's Chorus performed and Lincoln's desk was lined with patriot bunting.
"We're here to celebrate, family, commitment, equality, love, courage and community," Harris told the crowd to enthusiastic applause.
Comptroller Judy Baar Topinka, a Republican, praised the three House GOP members who voted in favor of the measure.
"History will show that we got it right on this one," she said before telling the crowd, "I am available to be a flower girl, and I'll even waive the fee."
When the law takes effect June 1, same-sex couples can begin applying for marriage licenses. And officials in Cook County -the state's most populous - have even said the facilities will be open for business that day even though it's a Sunday. There's a small chance weddings could take place before then; Legislation is pending that could change the effective date to immediately. Lawmakers aren't expected to come back to Springfield until January's end.
In the meantime, Illinois couples have already started planning.
Aimee Woolery from the Chicago suburb of Berwyn, has been with her partner for 15 years and attended the bill signing with the couple's two children.
"For us, it's the family piece of it, they get some more security," Woolery said, explaining that the couple decided against a civil union when Illinois legalized them. "We were holding out for marriage in Illinois."
Her 9-year-old daughter, Graysen, said she is excited for her moms to wed.
"I want him to be the ring bearer," she said pointing to her little brother. "And I want to be the flower girl."