[3][4] The county is home to the headquarters of the Three Affiliated Tribes of the Mandan, Hidatsa, and Arikara people, and a large part of the county belongs to the tribe's Fort Berthold reservation.The origin of its name came from Joseph Mountraille, a locally famed Metis voyageur and mail carrier from Pembina under Norman Kittson's employment.[4][10][11] Oil production from the Bakken formation in the early 21st century attracted workers and reversed decades of population decline in the county.The Missouri River flows southeastward along the SW boundary line of Mountrail County, and Shell Creek drains the lower central part of the county into the Missouri, discharging at Shell Creek Bay.Its highest point is on the upper west boundary line, at 2,480 ft (760 m) ASL.Bill Clinton won both of his terms, and Barack Obama carried this county in the 2008 election.