St. Mary is an unincorporated community on the western border of the Blackfeet Indian Reservation adjacent to Glacier National Park in Glacier County, Montana, United States. The village is the eastern terminus of the Going-to-the-Sun Road which bisects the park east to west, a distance of 53 mi. About 54 people reside in the village year-round; however, the population increases tenfold on a busy summer evening.