As of 2011, it had a population of 52,627 and an area of 4,019.97 square kilometres (1,552.12 sq mi).

The population density of the subprefecture, 13 people per km2, is very low compared to the rest of Japan.

[1][2] Rumoi Subprefecture stretches broadly across the coast of the Sea of Japan in northwestern Hokkaido.

The Rumoi River 44 kilometres (27 mi) flows from Mount Poroshiri in the Hidaka Mountain range to the Sea of Japan.

[3] Mashike Subprefecture was established as part of the administrative reforms of Hokkaido during the Meiji period (1868 – 1912).