Koumi (小海町, Koumi-machi) is a town located in Nagano Prefecture, Japan.

Mount Tengu (2646 meters) is located on the border of Koumi with Chino.

[3] Per Japanese census data,[4] the population of Koumi has declined over the past 60 years.

The area of present-day Koumi was part of ancient Shinano Province.

Koumi has a public high school operated by the Nagano Prefectural Board of Education.