Rumoi is a city located in the Rumoi Subprefecture of Hokkaido, Japan. It covers a total area of 297.81 square kilometers (114.99 square miles) and maintains a population density of approximately 61 people per square kilometer.
The name of the city is derived from the Ainu word for the Rumoi River. Specifically, it originates from the term "rur-mo-ot-pe," which translates to "a river with calm, constant tides" or "a river with deep tides." This etymological theory has been officially adopted by the city.