Kōshū is a city located in Yamanashi Prefecture, Japan. As of 1 September 2020, the city had an estimated population of 29,659 in 13,141 households, and a population density of 120 persons per km². The total area of the city is 264.11 square kilometres (101.97 sq mi). The city is the home of the indigenous Koshu grape and is synonymous with viticulture and wine production in Japan.

Yamanashi Prefecture is a prefecture of Japan located in the Chūbu region of Honshu. Yamanashi Prefecture has a population of 817,192 and has a geographic area of 4,465 km2. Yamanashi Prefecture borders Saitama Prefecture to the northeast, Nagano Prefecture to the northwest, Shizuoka Prefecture to the southwest, Kanagawa Prefecture to the southeast, and Tokyo to the east.