During the Edo period the area around Yamakita was part of Odawara Domain, along with most of western Sagami Province.

In the Meiji era, the town prospered as a transportation hub with the opening of the Tokaido Main Line railway, but when the line changed its route due to the opening of the Tanna Tunnel, its role rapidly declined.

Yamakita has a mayor-council form of government with a directly elected mayor and a unicameral town council of 14 members.

Yamakita, 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.