U.S. Route 87 (US 87) is a part of the U.S. Highway System that travels Port Lavaca, Texas, north to Havre, Montana. In the state of Montana, It extends approximately from the Wyoming state line near Wyola north to its terminus at US 2 near Havre.
US 87 enters Montana running concurrently with Interstate 90 (I-90) and travels westward for to Crow Agency, where US 212 merges with the route. The three routes continue westward for another to Billings, where it intersects with the western terminus of I-94 in suburban Lockwood. US 87 follows the I-90/US 212 concurrency for another before it heads north, following Main Street through Billings Heights. US 87 continues north for and intersects US 12, sharing a concurrency through Roundup. US 87 continues north with a slight bend to the northwest for until it intersects Montana State Highway 200 (MT 200) near Grass Range and takes a sharp turn west; US 87 remains concurrent with MT 200 until Great Falls. US 87 and MT 200 travel west for to Lewistown, where they merge with US 191 and continue heading generally westward. About west of Lewistown near Moore, it breaks with US 191 and merges with MT 3, where they head northwest for and merge with US 89 near Armington. The four-route concurrency of US 87/US 89/MT 3/MT 200 continues northwest for to Great Falls, where US 87 leaves all three and travels north through the city. North of Great Falls, US 87 travels northeast for to Fort Benton and a final to its terminus with US 2, about west of Havre.
US 87 originally ran northwest out of Great Falls towards the eastern border of Glacier National Park to the Canadian Border at the Piegan Border Crossing. This was changed in 1934, when US 89 was diverted to US 87's routing north of Great Falls. US 87 terminated in Great Falls until when it was extended to its current northern terminus near Havre.