Los Alamitos is a city in Orange County, California. The city was incorporated in March 1960. The population was 11,780 at the 2020 census, up from 11,449 at the 2010 census. The adjacent unincorporated community of Rossmoor uses the same 90720 ZIP code in its mailing address, but is not part of the city. The Los Alamitos Race Course is named for the city, but lies in the neighboring city of Cypress.