Los Alamos County is a county in the U.S. state of New Mexico. As of the 2020 census, the population was 19,419. The smallest county by area in the state, Los Alamos County was formerly administered exclusively by the U.S. federal government during the Manhattan Project, but it now has equal status to New Mexico's other counties. The county has two census-designated places: Los Alamos and White Rock.

Bandelier National Monument is a 33,677-acre (136 km2) United States National Monument near Los Alamos in Sandoval and Los Alamos counties, New Mexico. The monument preserves the homes and territory of the Ancestral Puebloans of a later era in the Southwest. Most of the pueblo structures date to two eras, dating between 1150 and 1600 AD.