洛斯阿拉莫斯县（Los Alamos County, New Mexico）是美国新墨西哥州中北部的一个县。面积283平方公里，是全州面积最小的县。根据美国2000年人口普查，共有人口18,343人。县治洛斯阿拉莫斯（Los Alamos）。

成立于1949年3月16日。县名来自县治。是洛斯阿拉莫斯国家实验室的所在。

Los Alamos County (Spanish: The Aspens) is a county in the U.S. state of New Mexico. As of the 2010 census, the population was 17,950. The smallest county in area of this state 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 county seat is Los Alamos. The other population center in the county is White Rock.