It is formed in
Glacier County in northwestern Montana, north of
Browning, Montana, by the confluence of its South and Middle forks. The long South Fork and long Middle Fork both rise in the
Rocky Mountains just east of
Glacier National Park, in the
Blackfeet Indian Reservation. Much of the water in the North Fork is diverted from the
St. Mary River through a canal and
inverted siphon. The main stream flows east-northeast into southern Alberta, where it is joined by the
North Fork of the Milk River, from there It flows past the town of
Milk River and
Writing-on-Stone Provincial Park, then turns southeast into Montana, running east along the north side of the
Sweetgrass Hills, turning south, passing through the
Fresno Dam, then east past
Havre and along the north side of the
Fort Belknap Indian Reservation. Near
Malta, it turns north, then southeast, flowing past
Glasgow and joining the Missouri in
Valley County, Montana, downstream from
Fort Peck Dam. The watershed of the river extends into the Canadian provinces of Alberta and
Saskatchewan and the US state of Montana. The watershed of the river covers an area of . Of this lies in Alberta, in Saskatchewan and the remaining in Montana.{{cite web == History ==