We examined the vascular flora of the Wachusett Mountain area in the towns of Princeton and Westminster, Massachusetts. The study area comprised the Wachusett Mountain State Reservation, Minns Wildlife Sanctuary, and a small municipal inholding, together covering 1275 ha. The summit of Wachusett Mountain, at 611 m, is the highest elevation east of the Berkshire Mountains in southern New England, and the site includes approximately 100 ha of old-growth forest and an active ski area. Using convenient physiographic features, we defined 34 sampling units in which we recorded all observed vascular plant species. Fieldwork took place during the 2019–2023 field seasons, with visits to each unit conducted systematically over the growing season. We also recorded information from more than 500 herbarium specimens previously collected from the mountain. In total, 861 species have been recorded from the mountain, of which 30% are nonnative. The total includes 10 state-listed and 18 watch-list species, an unusual concentration of rare species for central Massachusetts. Thirty-one species with historical records were not relocated by us. Numerous species show patterns of distribution related to elevation or slope/aspect, but most of these appear to reflect correlated variables, such as the presence of wetlands at lower elevations and the presence of ski trails on the north side of the mountain. Species indicative of site richness are heavily concentrated on the mountain's southern slopes, which we attribute to a combination of bedrock geology, glacial plucking, and colluvial processes. The ski trails support several dozen species not found elsewhere on the mountain, including three state-listed species.