Steller's Sea Cow was known from the Bering Sea. The last population was discovered by a Russian expedition wrecked on Bering Island in 1741. It is likely that a population also persisted in at least the western Aleutian Islands into the 18th century (Domning et al. 2007).

A catalogue of osteological specimens of H. gigas in the world’s museums, with a history of their collection, was published by Mattioli and Domning (2006).

In the Pliocene and Pleistocene, Hydrodamalis occurred from Japan to Baja California, Mexico (Domning 1978; Domning and Furusawa 1995), a range that coincided with that of the Sea Otter Enhydra lutris.