Los Alamos County /

Los Alamos County (Spanish: The Cottonwoods) is a county located in the U.S. state of New Mexico. In 2000, its population was 18,343. The Class H county/municipality was administered exclusively by the U.S. federal government during the Manhattan Project, but now has equal status to New Mexico's other counties. The seat of the county is at the townsite of Los Alamos. The other population center in the county is White Rock. The county is home to the Los Alamos National Laboratory. According to the U.S. Census Bureau, the county has a total area of 109 square miles (283 km²). Los Alamos County is by far the smallest county in New Mexico by area. There is no significant open water in the county. The county's highest point is located along its northern border, near the summit of Caballo Mountain, at 10,480 feet above sea level. As of the census of 2000, there were 18,343 people, 7,497 households, and 5,337 families residing in the county. The population density was 168 people per square mile (65/km²). There were 7,937 housing units at an average density of 73 per square mile (28/km²). The racial makeup of the county was 90.26% White, 0.37% Black or African American, 0.58% Native