Hachiōji Castle was a Sengoku period Japanese castle, located in what is now the city of Hachiōji, Tokyo, in the Kantō region of Japan Its ruins have been protected as a National Historic Site since 1951, with the area under protection extended in 2005.

Hachiōji is a city located in the western portion of Tokyo Prefecture, Japan. As of 31 March 2021, the city had an estimated population of 561,344, and a population density of 3,000 persons per km2. The total area of the city is 186.38 km2 (71.96 sq mi).