Understanding patterns of animal space use and range fidelity has important implications for species and habitat conservation. For species that live in highly seasonal environments, such as mountain goats (Oreamnos americanus), spatial use patterns are expected to vary in relation to seasonal changes in environmental conditions and sex‐ or age-specific selection pressures. To address hypotheses about sex, age, and seasonality influence on space use ecology, we collected GPS location data from 263 radio‐collared mountain goats (males, n = 140; females, n =123) in coastal Alaska during 2005 – 2016. Location data were analyzed to derive seasonal and sex‐specific fixed-kernel home range estimates, and to quantify the degree of seasonal range and utilization distribution overlap. Overall, we determined that home range size was  smallest during winter, expanded coincident with the onset of green-up and parturition, and were largest during summer. Home range size of males and females did not differ significantly during winter, but females had larger home ranges than males during summer; a relationship that was switched during the mating season. Pairwise comparisons involving individual females across subsequent years indicated home ranges were significantly smaller during years when they gave birth to offspring. Mountain goats exhibited a strong degree of range fidelity, and  99% (n =138) of individual animals returned to their previous year’s seasonal range with an average annual Bhattacharyya’s Affinity utilization distribution overlap index of 68%. Similarity of seasonal home range utilization distributions varied in relation to sex and season in some respects. Home range overlap was highest during the summer vegetation growing season, particularly among females. These findings advance our understanding about how environmental variation and sex- and age-related reproductive constraints influence space use and range fidelity among alpine ungulates. Documentation of the high degree of range fidelity among mountain goats has important conservation implications in landscapes increasingly altered by anthropogenic activities.