Koshi District, NiigataKoshi was a district located in Niigata Prefecture, Japan.As of 2003, the district had an estimated population of 2,035 with a density of 51.09 persons per km2. The total area is 39.83 km2.MunicipalitiesPrior to its dissolution, the district contained only one village: YamakoshiHistoryRecent mergers On April 1, 2005 - The village of Yamakoshi, along with the town of Oguni, the town of Nakanoshima, and the towns of Koshiji and Mishima, was merged into the expanded city of Nagaoka. Therefore, Koshi District was dissolved as a result of this merger.