From there the highway passes through the southern end of Glacier National Park and follows the Middle Fork of the Flathead River and the BNSF Railway line.

After crossing the Continental Divide at Marias Pass west of East Glacier, the highway exits the Rocky Mountains and begins its trek through the northern plains.

From here to the North Dakota border, the area surrounding the highway and the adjacent railroad is known as the "Hi-Line" to Montanans from the early Great Northern Railway route.

It next travels through Cut Bank and Shelby, where it meets Interstate 15 (I-15) and becomes the northern border of the area known as the "Golden Triangle", another colloquial region in Montana.

From Shelby, it hits a string of small towns before it goes on to Havre, near the geographical center of the road in the state and the other northern apex of the Golden Triangle.

The most notable reroutings from the original corridor are: 1) the section from Moyie Springs, Idaho, to just inside the Montana border, which once ran much further north, as seen on the 1937 map of the area[3] (Old US 2N intersects today's US 2 about 2.6 miles (4.2 km) east of the state line); 2) passing north of Kila; 3) a route swap with Secondary Highway 206 (S-206) between Evergreen and Columbia Falls in 1983 (as seen in the 1985 state map);[4] 4) widening the highway to three or four lanes between Hungry Horse and West Glacier in 1987 (as seen on page 35 of the 2013 road log); and 5) construction of a more direct route between East Glacier and Browning over the Two Medicine River (which eliminated the concurrency with US 89 between Kiowa and Browning).