Tōkamachi (十日町市, Tōkamachi-shi) is a city located in Niigata Prefecture, Japan. As of 1 July 2019, the city had an estimated population of 28,728 in 19,823 households, and a population density of 86.3 persons per km². The total area of the city was 590.39 square kilometres, although some borders of the city are not well defined. Tōkamachi derives its name from the fact that a market was held every tenth day of the month. Similarly, the nearby former town of Muikamachi had its own local market held on days ending in six each month.