Achi is a village located in Nagano Prefecture, Japan. As of 1 April 2019, the village had an estimated population of 6,379 in 2360 households, and a population density of 30.7 persons per km2. The total area of the village is 214.43 square kilometres (82.79 sq mi).

Nagano Prefecture is a landlocked prefecture of Japan located in the Chūbu region of Honshū. Nagano Prefecture has a population of 2,007,682 and has a geographic area of 13,561.56 square kilometres (5,236.15 sq mi). Nagano Prefecture borders Niigata Prefecture to the north, Gunma Prefecture to the northeast, Saitama Prefecture to the east, Yamanashi Prefecture to the southeast, Shizuoka Prefecture and Aichi Prefecture to the south, and Gifu Prefecture and Toyama Prefecture to the west.