Los Alamos County is a county in New Mexico, United States, on the Pajarito Plateau above the Rio Grande. It had a population of 19,419 at the 2020 census and covers 109 square miles (280 km2) centred near 35°52′N 106°19′W.<\/p>\n
Los Alamos is the county seat and largest community; its postal code is 87544. The county has two census-designated places — Los Alamos and White Rock — and no incorporated towns or cities, since the county itself performs municipal functions. It observes Mountain Time and carries FIPS code 35028.<\/p>\n
Los Alamos County has just two named census-designated places, both unincorporated under New Mexico law but governed directly by the county’s combined city-county administration. A handful of older place names from the plateau’s ranch-school and wartime era, including Upper Frijoles Crossing, survive on maps but no longer function as populated settlements.<\/p>\n
| Place<\/th>\n | Type<\/th>\n | Pop.<\/th>\n | ZIP<\/th>\n<\/tr>\n<\/thead>\n |
|---|---|---|---|
| Los Alamos<\/td>\n | CDP · seat<\/td>\n | 13,179<\/td>\n | 87544<\/td>\n<\/tr>\n |
| White Rock<\/td>\n | CDP<\/td>\n | 5,852<\/td>\n | 87547<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nZIP Codes<\/h2>\nNearly all county addresses fall under these two ZIP codes; there is no separate code for the sparsely populated western and southern portions of the county.<\/p>\n Geography<\/h2>\nThe county sits on the volcanic Pajarito Plateau, cut by deep, steep-walled canyons that drain east toward the Rio Grande. Elevations range from roughly 5,600 feet in the canyon bottoms to over 10,000 feet in the Jemez Mountains along the county’s western edge, inside the Valles Caldera. Bandelier National Monument covers much of the southern county. Los Alamos County is New Mexico’s smallest county by land area and borders Rio Arriba County to the north, Santa Fe County to the east, and Sandoval County to the south and west.<\/p>\n Demographics<\/h2>\nThe county’s population of 19,419 at the 2020 census is split between Los Alamos, the larger community, and White Rock. Household income here has long ranked among the highest of any county in the United States, well above the New Mexico median of $62,268, reflecting the concentration of scientists, engineers, and federal contractors employed at the national laboratory. Population density is about 178 people per square mile, low by national standards given the amount of undeveloped canyon and forest land within the county.<\/p>\n Economy & Local Life<\/h2>\nLos Alamos National Laboratory is the county’s dominant employer by a wide margin, supporting nuclear weapons research, materials science, and other federal programs, and drawing a workforce with one of the highest concentrations of PhDs of any U.S. county. Beyond the lab, the local economy runs on the services, schools, and retail that support that workforce. The Los Alamos Historical Museum and the Bradbury Science Museum, both downtown, are the county’s main visitor draws, alongside hiking and skiing in the surrounding Jemez Mountains.<\/p>\n History<\/h2>\nLos Alamos County was organized on June 10, 1949, carved out of parts of Sandoval and Santa Fe counties. Before that date the area had been administered directly by the federal government since 1943, when the U.S. Army seized the Los Alamos Ranch School to build the secret laboratory that developed the first atomic bombs under the Manhattan Project. The county’s name comes from the Spanish for “the poplars” or “the cottonwoods.” The 2000 Cerro Grande Fire, started as a prescribed burn that escaped control, destroyed several hundred homes in Los Alamos before the town was rebuilt.<\/p>\n Getting There<\/h2>\nNM 502 connects Los Alamos to US 285\/84 near Pojoaque, and NM 4 runs south through White Rock toward Bandelier and the Jemez Mountains.<\/p>\n
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