Box Elder is an unincorporated community and census-designated place in Hill County in the U.S. state of Montana. The population was 87 at the 2010 census. The population was 794 at the 2000 census, but before 2010 the Box Elder CDP was split into the current much-smaller Box Elder CDP, while most of the former CDP area went into the new Rocky Boy West CDP. Box Elder is the headquarters of the Chippewa-Cree tribe. The post office was established in 1889.