Mollie Wagoner, a 20-year-old college student from St. Mary's County, and her girlfriend, Sharon Burk, woke up early to wait outside the court. Wagoner described the anticipation and excitement in the crowd as "infectious."
"This is by no means the end," said Wagoner, who attends American University in Washington. "It's great to celebrate today, and tomorrow we still have work to do."
Bea Blacklow of Silver Spring joined her gay son, Mark, outside the court.
"It's going to mean a lot for a lot of people," said Blacklow, 64. "More, maybe, than anyone knows."
But significant practical questions remain about how benefits will begin — and how soon.
The Obama administration must review statutes and regulations before opening benefits up to same-sex spouses. And it's not yet clear whether certain benefits would be revoked if a married gay couple moved to a state that did not recognize their marriage — say, from Maryland to Virginia.
The Social Security Administration and the Office of Personnel Management, which oversees benefits for federal employees, said Wednesday they would work to answer those questions quickly.
Defense Secretary Chuck Hagel said the Pentagon "welcomes" the ruling on the Defense of Marriage Act and would work to make benefits available to same-sex spouses "as soon as possible."
University of Maryland law professor Martha Ertman said the decision will bring new responsibilities as well as new benefits. Some might pay more in federal taxes. Ethics laws requiring certain federal employees to disclose spousal income will now also apply to gay couples.
Reaction to the rulings on Capitol Hill was mixed, with most Democrats cheering the decisions and many Republicans saying they were disappointed but committed to fighting for the traditional definition of marriage in state capitals.
House Minority Leader Nancy Pelosi of California said the decision "bent the arc of history once again toward justice." Speaker John Boehner, an Ohio Republican, vowed that a "robust national debate over marriage will continue in the public square."
Maryland Democrats, including Sens. Barbara A. Mikulski and Ben Cardin, issued statements applauding the decision. Cardin said the court "made whole" loving families across the nation. Mikulski said she was "proud to see the day that marriage equality becomes the law of the land."
Baltimore Rep. Elijah E. Cummings described the ruling as "a critical next step in ensuring that all Americans are treated equally under the law."
All three, as well as Rep. Steny Hoyer of Southern Maryland, had joined a majority of their party in supporting the Defense of Marriage Act in 1996.
Rep. Andy Harris, the sole Republican in Maryland's congressional delegation, said he is glad the Supreme Court upheld the rights of states to define marriage. But the Baltimore County lawmaker expressed disappointment that "the unelected Court overruled the will of the elected Congress on this issue."
Still, it's unlikely that today's Congress would have supported the Defense of Marriage Act — or even been willing to bring the issue to a floor vote — in part because public opinion on the issue has shifted so dramatically in the nearly two decades since President Bill Clinton signed the bill into law.
Fifty-three percent of Americans believe marriages between same-sex couples should be recognized by the law, up from 48 percent in 2011 and 27 percent in 1996, according to a Gallup poll last month.
The justices joining Kennedy in the majority opinion were Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan. Three justices wrote dissenting opinions: Chief Justice John Roberts; Antonin Scalia and Samuel Alito.
Roberts wrote that Congress acted constitutionally when it passed DOMA.
"Interests in uniformity and stability amply justified Congress's decision to retain the definition of marriage that, at that point, had been adopted by every state in our nation, and every nation in the world," he wrote.
Hours after the decision was announced, Sotomayor was seen strolling down Main Street in Annapolis.
State Sen. Richard S. Madaleno Jr., the only openly gay member of his chamber and a Montgomery County Democrat instrumental in passing Maryland's same-sex marriage law, said he stopped Sotomayor, hugged her, and introduced her to his 6-year-old son.
"When do you ever get a chance to run into a Supreme Court justice and say thank you for what you've done?" he said later.
Sun reporters Kevin Rector, Erin Cox, Carrie Wells and the Tribune Washington bureau contributed to this article.