Chicago, which has never held an Olympics, now will try to persuade the International Olympic Committee that it deserves to be the host, joining a group of bidders expected to include Madrid, Prague, Rome, Rio de Janeiro and Tokyo.
"It was a very tough decision," USOC chairman Peter Ueberroth said before opening a sealed envelope and revealing the winning city. "If I had all the power — and sometimes people accuse me of that — I would take the map and merge the two cities, because I'll tell you what: If you could take the mayors of these two communities and have them run our country, we would all be better off."
The IOC will award the 2016 Games in October 2009.
"It's just beginning," said Patrick Ryan, Chicago's bid committee chairman. "It's a long road."
The USOC had said beforehand it would not release Saturday's vote count.
By choosing Chicago instead of Los Angeles, the 11-member USOC board of directors went with a city that does not have major venues already in place. Los Angeles held the Summer Games in 1984 — when the Olympics were run by Ueberroth — and in 1932.
Chicago, meanwhile, offered a bid that hinges on building new facilities, mostly situated around the downtown lakefront and nearby parks. The centerpiece would be an 80,000-seat, $366 million temporary Olympic stadium that would be built in historic Washington Park. Chicago's plans also call for a $1.1 billion lakefront village that would be built near the convention center just south of downtown.
"This is a wonderful and very important thing for our city," Ryan said.
The lack of ready-to-go venues apparently did not dissuade the USOC during its board meeting at a hotel Saturday, despite what happened the last time the IOC was looking for a Summer Games site.
New York City appeared to be a front-runner for the 2012 Olympics until financing for a new stadium in Manhattan fell apart just weeks before the final vote. New York wound up with only 16 of 60 votes needed, and London landed those Olympics.
That led the USOC to revamp its domestic selection process. Led by Ueberroth, the USOC has insisted that financing be in place and transparent, and that governments be willing to provide guarantees for the bids if private money doesn't cover all costs.
Both the city of Chicago and the state of California complied. Ryan also said Saturday that an insurance company is pledging to provide a $500 million policy to cover revenue shortfalls and cost overruns, though not related to completion of venues.
"The legacy projects, coupled with the guarantees they have offered, I believe gave our board a level of assurance that might have been the differentiation between the cities," USOC international vice president Bob Ctvrtlik said.
The USOC's process for 2016 began a year ago, with Houston, Philadelphia and San Francisco also in the running. Houston and Philadelphia were eliminated by the USOC last July, and San Francisco dropped out in November.
After Saturday's announcement, Ueberroth spoke about the importance of the U.S. candidate having success when the IOC picks a 2016 host.
Chicago is considered to have a good shot against its international competition, because, by 2016, 20 years will have passed since the last time the United States hosted the Summer Olympics — at Atlanta in 1996.
Also, a U.S. bid for 2016 could be helped by the idea of geographic rotation, because the IOC picked European cities for the Summer Olympics of 2004 (Athens) and 2012 (London), and an Asian city (Beijing) for 2008.