[2] It lies along the United States border with Canada, abutting Alberta and Saskatchewan.

Part of its territory is within the Rocky Boy Indian Reservation, which is held by the federally recognized Chippewa-Cree Tribe.

The first European-American settlement in the future county area was Fort Assinniboine, garrisoned by the United States Army in 1879.

The county is named after James J. Hill, president of the Great Northern Railway Company, which built the rail line across Montana as part of the Transcontinental Railroad to the Pacific coast.

It is one of the few locations in the United States to have an antipodal point on land, and its community of Rudyard is the only populated such place.

The Kerguelen Islands are on the opposite side of the earth from parts of Hill County, while the antipodal points of almost all other places in the United States lie in the Indian Ocean.