MT 87 begins at the Montana-Idaho state line, traveling through Raynolds Pass. The highway proceeds northward, intersecting a small road before entering rural areas within Gallatin National Forest. The route continues northeast, intersecting several forest roads before bending northwestward. The route intersects several small roads while it runs parallel to a small creek. It crosses over the Madison River after passing several small buildings. The highway continues northwestward to its northern terminus, an at-grade intersection with US 287. The highway is maintained by the Montana Department of Transportation (MDT). Part of the job of the MDT is to measure traffic along the highway. These counts are taken using a metric called annual average daily traffic (AADT). This is a statistical calculation of the average daily number of vehicles that travel along a portion of the highway. In 2011, the MT 87 had an AADT count of 583 vehicles. No portion of the highway is listed as part of the National Highway System (NHS), a network of roads important to the country's economy, defense, and mobility.