Kosmoceratops, along with most other chasmosaurines, inhabited Laramidia, an island continent at the time that now forms western North America. During the Late Cretaceous, Laramidia was separated from Appalachia, the eastern North American landmass, by the Western Interior Seaway. A major evolutionary radiation took place on Laramidia, with many major dinosaur clades known from across the island continent. Two endemic faunas may have existed in separate biomes or "provinces": one to the south of what is now Utah and Colorado, and one north of this region. Kosmoceratops, along with most other Campanian chasmosaurines, lived in the southern province, while the north was only inhabited by species of Chasmosaurus that existed in what is now Alberta.