[1] The total area of the city is 53.19 km2 (20.54 sq mi)..[2] Kōshi is located in a northern inland part of Kumamoto Prefecture.

Kumamoto Prefecture Kōshi has a humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

After the Meiji restoration, the villages of Kōshi and Nishikōshi was established with the creation of the modern municipalities system on April 1, 1889.

[4] Kōshi has a mayor-council form of government with a directly elected mayor and a unicameral city council of 19 members.

In terms of national politics, the city is part of the Kumamoto 3rd district of the lower house of the Diet of Japan.