Sunagawa is a city located in Sorachi Subprefecture, Hokkaido, Japan. As of September 2016, the city has an estimated population of 17,589 a…Sunagawa is a city located in Sorachi Subprefecture, Hokkaido, Japan. As of September 2016, the city has an estimated population of 17,589 and a population density of 220 people per km². The total area is 78.69 km².