Little information exists concerning the distribution of fruit flies in the genus Rhagoletis Loew, 1862 (Diptera: Tephritidae) in Montana, western U.S.A. Here, the presence of and host plant use by Rhagoletis spp. are documented in northwestern Montana. The western cherry fruit fly, Rhagoletis indifferens Curran, 1932, was abundant in the state and infested sweet cherry, Prunus avium (L.) L.; mahaleb cherry, P. mahaleb L.; tart cherry, P. cerasus L.; and bitter cherry, P. emarginata (Douglas ex Hook.) D. Dietr. (Rosaceae). Black cherry fruit fly, R. fausta (Osten-Sacken, 1877), was rare and detected only in bitter cherry. Rhagoletis berberis Curran, 1932, R. basiola (Osten-Sacken, 1873), R. tabellaria (Fitch, 1855), and apple maggot, R. pomonella (Walsh, 1867), were all recorded for the first time in Montana. Flies in Montana were mainly reared from previously reported species of host plants, but new host records also documented include, R. indifferens from black hawthorn, Crataegus douglasii Lindl. (Rosaceae), a new Montana record; R. berberis from sweet cherry; R. basiola from baldhip rose, Rosa gymnocarpa Nutt. (Rosaceae); and R. tabellaria from Hooker's fairy bells, Prosartes hookeri Torr. (Liliaceae). Rhagoletis pomonella, likely introduced into the western U.S., was reared from C. douglasii but not from the relatively few domesticated apple trees, Malus domestica Borkh., (Rosaceae) sampled. The findings extend the known geographic ranges of four Rhagoletis species and indicate that some flies in northwestern Montana have the ability to survive and develop in alternative and novel hosts, consistent with findings for populations in other areas of the western U.S.