Nagano is the capital and largest city of Nagano Prefecture, located in the Nagano Basin in the central Chūbu region of Japan. Nagano is categorized as a core city of Japan. Nagano City is the highest prefectural capital in Japan, with an altitude of 371.4 meters (1,219 ft). The city is surrounded by mountains, the highest of which is Mount Takatsuma (2,353 m), and it is near the confluence of the Chikuma River—the longest and widest river in Japan—and the Sai River. As of 1 July 2023, the city had an estimated population of 365,296 in 160,625 households, and a population density of 438 persons per km². The total area of the city is 834.81 square kilometres (322.32 sq mi).

The Shinano River , known as the Chikuma River in its upper reaches, is the longest and widest river in Japan and the third largest by basin area. It is located in northeastern Honshu, rising in the Japanese Alps and flowing generally northeast through Nagano and Niigata Prefectures before emptying into the Sea of Japan. It is designated as a Class A river.