The opening ceremony will be July 14. Competition will run through July 30. The Paralympic Games will be Aug. 15-27.
"This milestone makes the games real for every athlete actively training for their LA28 dream and the fans who follow the journey,” said LA chief athlete officer Janet Evans, a five-time Olympic medalist swimmer.
Los Angeles previously hosted the Olympics in 1984 and 1932.
International Olympic Committee President Thomas Bach was on hand for the announcement. He visited future venues and met with LA28 leadership.
“I have been really impressed by the progress and creativity of the LA28 team,” Bach said.
“They are using the power of the Olympic Games to inspire young people to get involved in sport.”
The Games will use existing stadiums and venues across the region. The organizing committee said 15,000 athletes are expected to compete in both the Olympic and Paralympic games.