Los Alamitos is a small city in Orange County, California. The city was incorporated in March 1960. The population was 11,449 at the 2010 census, down from 11,536 at the 2000 census. It is often mistakenly thought to include the adjacent but unincorporated community of Rossmoor, which uses Los Alamitos as its mailing address. The Los Alamitos Race Course is also widely believed to be in the city; although it does have a Los Alamitos postal address and zip code, it actually lies in the neighboring city of Cypress.The USA Water Polo National Aquatic Center is located on the Joint Forces Training Base - Los Alamitos.