Rumoi Subprefecture (留萌振興局, Rumoi-shinkō-kyoku) is a subprefecture of Hokkaido Prefecture, Japan. 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. The population of Rumoi Subprefecture represents 0.96% of the overall population of Hokkaido.