Since November, Minnesota went from defeating constitutional amendment that would have defined marriage as between a man and a woman to becoming the third state in 2013 to enact same-sex marriage laws. While the Minnesota amendment failed on Election Day 2012, voters in Maryland, Washington and Maine approved same-sex marriage initiatives.
In early May, Delaware Gov. Jack Markell, a Democrat, signed a same-sex marriage bill into law.
What are some of the factors in more states recognizing same-sex marriages?
"Attitudes toward lesbian, gay and bisexual people have steadily become more favorable over the last couple of decades" and are having a long-term effect, said M.V. Lee Badgett, an expert on same-sex marriage policy issues, professor of economics and director of the Center for Public Policy and Administration at the University of Massachusetts-Amherst. "One reason is that more and more LGB people are open about their sexual orientation, giving heterosexual people a chance to get to know LGB people and learn about their lives."
Also, more public figures have announced their sexual orientation and many heterosexual allies of the LGB community have announced their support for gay marriage.
"Another long-term change that is important in the U.S. context is that businesses have increasingly recognized employees' same-sex couples for purposes of healthcare benefits, a trend that is also related to more openness and organizing by LGB people in the workplace," Badgett said.
Minnesota's law, effective Aug. 1, specifies marriage is a civil contract between "two people" rather than "a man and woman" -- language that had been on the books since 1977. It removes same sex-marriage from a list of "prohibited marriages, and allows Minnesota to recognize same-sex marriages from other states. It also provides protections to clergy and other religious organizations that don't want to solemnize same-sex marriage.
"My partner and I have been together for 25 years," Mary Hartmann, 65, of St. Paul told the St. Paul Pioneer Press. "We raised three children and have two grandchildren."
"And now we can stop living in sin."
A recent Gallup survey indicated 53 percent of Americans said the law should recognize same-sex marriages -- the third consecutive reading at 50 percent or higher during the past year.
The 53 percent in favor ties the high to this point, measured both last November and in May 2011.
Just three years ago, support for gay marriage was 44 percent, the Princeton, N.J., polling agency said. The 53 percent show of support is nearly double the 27 percent in Gallup's initial measurement on gay marriage in 1996.
On the day the Minnesota Senate took up the gay marriage bill, St. Paul Mayor Chris Coleman proclaimed May 13-17 "Freedom to Marry Week," with pride flags lining the Wabasha Street Bridge, which was temporarily renamed the "Freedom to Marry Bridge."
The city's proclamation said St. Paul was proud of its "long history of fighting for civil and human rights for all people."
"We should not legislate against the freedom of caring, mature adults to marry the person he or she loves," the proclamation said.
"Letting same-sex couples marry saves money for governments -- low income same-sex couples need less help from the state, and the state gets a boost in tax revenue when gay people spend money on their weddings," Badgett said about what recognizing gay marriage could mean for a state's bottom line. "In Minnesota, for example, we predicted that the state would see $42 million in new business spending, and that would generate $3 million in tax revenue for state and local governments."
While 12 states recognize gay marriage, 30 states have constitutional amendments or voter-approved propositions banning same-sex marriage, which would have to be reversed to change the law.
Brian Brown, president of the National Organization for Marriage, which opposes gay marriage, said voters in many states are still unwilling to give up the traditional definition of marriage.
"We're not discouraged," he told The New York Times. "The states that have passed same-sex marriage are deep-blue liberal states."
Badgett said Illinois and New Jersey are states she'd watch because they have active legislative efforts going on and lawsuits challenging the exclusion of same-sex couples from marriage.
The South, though, is a tougher sell, she said, noting one study indicated Virginia and Florida have the most favorable opinion toward same-sex marriage.
"Public opinion in many states in the South suggests that it won't change right away," Badgett said. "But public opinion is changing rapidly for both older people and young people, so I would not be surprised to see even conservative states moving toward giving at least some rights to same-sex couples soon."
Minnesota joins Connecticut, Delaware, Iowa, Maine, Maryland, Massachusetts, New Hampshire, New York, Rhode Island, Vermont and Washington that legally recognize same-sex marriage.
The District of Columbia and three American Indian tribes have also legalized same-sex marriage. California, which granted same-sex marriages in 2008, now recognizes them on a conditional basis.
"I think Minnesota's actions could help boost the chances of marriage equality being enacted in Illinois," Badgett said. "It's definitely a sign that change is not just happening on the liberal West Coast and in New England states."
The U.S. Supreme Court heard arguments this term on two gay marriage-related appeals, one concerning the California Marriage Protection Act that says, in part, "Only marriage between a man and a woman is valid or recognized in California."
The second challenge is against the federal Defense of Marriage Act that says federal benefits and considerations for married couples apply only to heterosexual unions.