Harlem is a city in Blaine County, Montana, United States. The population was 769 at the 2020 census. The Fort Belknap Indian Reservation is just south of the town, across the Milk River. Like other towns along the Hi-Line, Great Northern Railway officials chose the name of a European city for this new town. In this case it was Haarlem, in the Netherlands. A. A. Cecil platted the townsite in 1889.