Due to the landslide caused by the 1923 Great Kanto Earthquake, the river in the north was blocked and Lake Shinsei.

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

Nakai has a mayor-council form of government with a directly elected mayor and a unicameral town council of 13 members.

Nakai, together with the other municipalities in Ashigarakami District and Minamiashigara city, collectively contributes one member to the Kanagawa Prefectural Assembly.

In terms of national politics, the town is part of Kanagawa 17th district of the lower house of the Diet of Japan.