(CNN) -- Illinois is poised to become the 15th state to allow same-sex marriage after legislation passed both houses of the state's General Assembly on Tuesday.
The bill now goes to Democratic Gov. Pat Quinn, who has said he will sign it.
The passage of the legislation "put our state on the right side of history," Quinn said.
President Obama also hailed the vote in his home state, saying he has "always believed that gay and lesbian Americans should be treated fairly and equally under the law.
"Over time, I also came to believe that same-sex couples should be able to get married like anyone else," he said.
"As I said in my Inaugural Address last January, our journey as a nation is not complete until our gay brothers and sisters are treated like anyone else under the law, for if we are truly created equal, then surely the love we commit to one another must be equal as well," the President added.
The law would take effect on June 1, 2014.
Illinois previously offered civil unions, but not marriage, to same-sex couples. In addition to Illinois, same-sex marriage is legal in 14 states -- California, Connecticut, Delaware, Iowa, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Rhode Island, Vermont and Washington -- as well as the District of Columbia. Colorado and Hawaii allow civil unions.
Same-sex marriage is banned in every state not mentioned above, except for New Mexico, which has no laws banning or allowing it.
Hawaii could become the next state to legalize same-sex marriage. Its Senate passed a bill in October, kicking it to the House, which is expected to vote soon.
Proponents of same-sex marriage say they have momentum on their side.
In June, the Supreme Court rejected parts of the Defense of Marriage Act in a 5-4 decision, dismissing an appeal over same-sex marriage on jurisdictional grounds and ruling same-sex spouses legally married in a state may receive federal benefits.
It also ruled that private parties do not have "standing" to defend California's voter-approved ballot measure barring gay and lesbians couples from state-sanctioned wedlock, clearing the way for same-sex marriages in California to resume.
But opponents say the fight is far from over.
Shortly before the Illinois votes, the president of the National Organization for Marriage urged people to contact their state representatives to tell them they support marriage as the union of one man and one woman.
"We've seen how marriage redefinition leads to those who believe in traditional marriage being punished, labeled 'bigots' and 'haters' in the public square, and forced to be silent about their deeply held beliefs or face repercussions. And their children? They're taught in schools that the values planted in them at home are bigoted and outdated, the equivalent of racism!" Brian Brown wrote in a blog post.
Worldwide, 16 other countries (and parts of Mexico) also have laws allowing same-sex marriage and domestic partnerships. Most of these are in Europe and South America.
CNN's Cristy Lenz contributed to this report.