But a sense of starting fresh remained elusive for many, who wondered what sort of legacy would begin on Jan. 1.
"Nothing seems to be going well," said John O'Donnell, of Hazleton, Pa. "People are losing their lives overseas. People are unemployed. It doesn't seem like it's about to end soon."
Las Vegas welcomed some 315,000 revelers with fireworks from casino rooftops, celebrity toasts at nightclubs and a traffic-free Las Vegas Strip.
David Fraley attended a separate gathering in Sin City's downtown estimated at 35,000 people.
"This decade's over. Let's get a better one going," said Fraley, 56, who lost his job as a supermarket liquor clerk in March.
Bob Batchelor, a professor of mass communications at Kent State University and author of "The 2000s," published before the decade was even done, said the meaning of the new decade would be "diminished by the hangover of the last decade."
"That," he said, "makes it tough to be as optimistic as Americans usually are."
But New York Mayor Michael Bloomberg was more tempered in his assessment.
"If you put it in the context of what people are suffering around the world, we're in very good shape," he said from Times Square.
Some were hopeful.
"I have many wishes for 2010!" exclaimed Ramona Vlada, 28, of Romania. "I wish to be healthy, love and to be loved at the same time, be with the family and make a family even bigger."
Celebrations took many forms, with concerts, fireworks and the timed drops of favorite local symbols.
Denver revelers by the thousand gathered downtown and gave the traditional New Year's countdown, ending with a rousing cheer as the clock struck midnight.
In the Tennessee cities of Memphis and Nashville, organizers dropped 10-foot red guitars. In Atlanta, an 800-pound fiberglass peach took a 138-foot plunge. In Times Square it was an 11,875-pound ball covered with more than 32,000 bulbs that was lowered at midnight.
In Boston, more than 1,000 artists and performers participated in the First Night celebrations. Artists planned to display six ice sculptures, including a replica of one of the Boston Museum of Fine Art's 4,000-year-old Egyptian sculptures.
And in Chicago, the city's Transit Authority was offering rides for a penny to help residents and visitors get in place for fireworks displays during the evening and at midnight.
Around the world, from fireworks in Sydney to balloons sent aloft in Tokyo, merrymakers at least temporarily shelved worries about the future to bid farewell to the first decade of the 21st century.
In Times Square, organizers mixed about 10,000 handwritten wishes into the 3,000 pounds of confetti that was dropped over the crowds. The messages included appeals for the safe return of troops fighting overseas, continued employment and a cure for diabetes.
The hundreds of thousands of people gathered brought out heightened police security, displayed a day earlier when officers evacuated several blocks around Times Square to investigate a parked van without license plates. Only clothing and clothes racks were found inside.
Police Commissioner Raymond Kelly, speaking from Times Square on a Webcast, said his department had many officers in the crowd, both uniformed and plainclothes.
He said officers were using bomb-sniffing dogs and technology to detect biological and chemical agents. Counter-sniper teams were set up as well.
As of early morning on the first day of the new decade, there had been no reports of trouble or arrests.