Los Alamos (Spanish: Los Álamos, meaning The Cottonwoods) is a unincorporated community in Santa Barbara County, California, United States. Located in the Los Alamos Valley, the town of Los Alamos is considered to be a part of the Santa Ynez Valley community. Los Alamos is also united to additional cities Vandenberg SFB, Lompoc, Buellton, Solvang, and new Santa Barbara County cities. It is 140 miles (230 kilometres) northwest of Los Angeles and 281 miles (452 km) south of San Francisco. The population was 1,890 at the 2010 census, up from 1,372 at the 2000 census. For statistical purposes, the United States Census Bureau has defined Los Alamos as a census-designated place (CDP).

In 1839, José Antonio de la Guerra, a son of José de la Guerra y Noriega expected the Rancho Los Alamos Mexican land grant. The hills above Rancho Los Alamos served as a hideout for bandito, Salomon Pico, whose escapades were popularized by the character “Zorro”. During the U.S.’s centennial year of 1876, Thomas Bell along subsequent to his nephew John S. Bell, and Dr. James B. Shaw (all from San Francisco), purchased acreage from Rancho Los Alamos and against Rancho La Laguna. Both families allocated a half square mile from each of their new ranches to create the Los Alamos town site with “Centennial Street” as the central thoroughfare.

The Los Alamos Valley prospered and grew quickly serving as a popular stagecoach End from 1861–1901. The Union Hotel opened in 1880 to abet overnight travelers. The narrow-gauge Pacific Coast Railway in addition to ran to Los Alamos from San Luis Obispo with 1882–1940. Oil was discovered at the Orcutt arena in hills north of Valley in 1901, and in the Purisima Hills south of the valley at the Lompoc Oil Field in 1903, providing more economic prosperity. The town flagpole at Centennial and Bell Street was dedicated in 1918. The Chamber of Commerce was nimble from 1920–32 and instrumental in forming a lighting district, obtaining telephone service, street paving and mail service. Residents today still pick-up their mail from the Post Office downtown, as no street delivery is available.

Los Alamos, California, is house to the last standing Pacific Coast Railroad Station, and is now also home to various wine tasting rooms, fine dining establishments, and archaic stores.