Paddlefish Polyodon spathula inhabiting Fort Peck Reservoir and the upper Missouri River, Montana, are members of the northern-most and western-most isolated group of the species. These isolated fish support a recreational, river-based snag fishery on migratory adults. We provide population demographics for the Fort Peck Paddlefish stock, including age structure, growth, reproductive success, recruitment, and population trends developed from creel surveys, adult fish tagging, and reservoir surveys of age-0 and age-1 fish over the period 1992-2020. Of 5,108 fish (2,560 males; 2,558 females), mean annual male age ranged from 18.5 to 21.5 years; mean age of females ranged from 24.3 to 30.8 years. Males did not mature until at least 9-12 years, whereas females did not mature until at least ages 16-19. Females were longer and much heavier than males at a given age and throughout adult life. Males exhibited both annual and biennial spawning, whereas almost no females showed consecutive-year spawning but commonly showed biennial spawning. Annual survival rates estimated from cumulative catch curves were 85% for males and 88% for females. Low counts of age-0 and age-1 fish in the reservoir as well as the modest numbers of young male recruits to the fishery indicate that the Fort Peck stock is characterized by a fairly steady but modest recruitment. This isolated stock continues to be managed as a recreational fishery with harvest while maintaining adult population size, sex, and age structure consistent with its recruitment.The Paddlefish Polyodon spathula, an ancient, filterfeeding zooplanktivore of the Mississippi and Missouri River drainages (Russell 1986;Grande and Bemis 1991;Jennings and Zigler 2009), has declined in abundance in many portions of its range in the past century as a result of dams (Hoover et al. 2019), large-river habitat alterations (Sparrowe 1986), and overfishing (Bettoli et al. 2009). Peripheral declines (i.e., edges of the native range) have been especially obvious (Gengerke 1986). In peripheral locations, initial numbers were often lower than in