(CNN) -- Hawaii's legislature gave final passage to a measure Tuesday to make it the 16th American state to legalize same-sex marriage.
"With today's vote, Hawaii joins a growing number of states that recognize that our gay and lesbian brothers and sisters should be treated fairly and equally under the law," President Obama, a native Hawaiian, said in a statement.
Illinois is poised to become the 15th state when its governor signs a same-sex marriage bill given final passage by its General Assembly last week. Democratic Gov. Pat Quinn has said he would "put our state on the right side of history" by signing it November 20.
Hawaii's Gov. Neil Abercrombie will sign the legislation Wednesday morning. The law is set to take effect on December 2.
"Whenever freedom and equality are affirmed, our country becomes stronger," Obama said. "By giving loving gay and lesbian couples the right to marry if they choose, Hawaii exemplifies the values we hold dear as a nation. I've always been proud to have been born in Hawaii, and today's vote makes me even prouder. And Michelle and I extend our best wishes to all those in Hawaii whose families will now be given the security and respect they deserve."
In addition to Hawaii and 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.
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 did not have standing to defend California's voter-approved ballot measure barring gay and lesbian 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.