Will Ditto, 25, a legislative aide, said he was getting ready to go to bed Sunday night when his mom called him with the news. He decided to leave his home on Capitol Hill and join the crowd. As he rode the Metro subway system to the White House, he told fellow passengers the news.
"It's huge," he said. "It's a great day to be an American."
George Washington University student Alex Washofsky, 20, and his roommate Dan Fallon, 20, joined the crowd.
"George Bush said, 'Bring him to justice, dead or alive,' and we did it," said Washofsky, a junior and a member of the Navy Reserve Officer Training Corps.
The crowd began gathering before President Barack Obama addressed the nation at about 11:30 p.m. Sunday. By midnight, people had filled a street directly in front of the White House and the celebration was spilling over into Lafayette Park to the north.
Some people sprinted up on foot to join the crowd. Others arrived on bicycles, and some people brought dogs.
American flags of all sizes were being held aloft, worn draped over the shoulders or gripped by many hands for a group wave. Some people climbed trees and lampposts to better display the flags they carried. Others without flags simply pumped their fists in the air.
One handmade sign said, "Ding-dong. Osama Bin Laden is dead!!!" Someone held a life-size cardboard cutout of Obama.
The impromptu street party took on aspects of a pep rally, at times. Some people offered up the "hey, hey, good-bye" sing-song chant more typically used to send defeated teams off to their locker rooms. And Parth Chauhan, 20, a sophomore at George Washington University, trumpeted a vuvuzela.
Chauhan was in fifth grade when the World Trade Center towers were attacked on Sept. 11. The Staten Island resident said he could see smoke from Ground Zero from his house for months. He said being in front of the White House early Monday felt like a good bookend to an era.
"I never really expected this day to come," he said.
Chauhan said he stopped studying for a human rights exam to join the crowd.
"School stopped when 9/11 happened. Now, it's stopping again, it seems," he said.
Henry Lee, 59, and his daughter Erin Lee, 30, of Van Nuys, Calif., came out to see the crowd after watching the president's speech on television.
"I've never seen anybody so happy over someone's death," said Henry Lee, who was in town to lobby on healthcare issues. "Justice has been done."
But Erin Lee said she was also worried.
"I'm kind of afraid about what's next, though," she said. "Are they going to retaliate against us?"
She said that the "war on terror" is "not necessarily over because Bin Laden is dead."