From the beginning of the 16th century the Hojo clan of Odawara expanded into the Kanto Plain. Hachioji Castle was built to guard the Kobosatsu Pass between Kai Province and the Kanto.

In 1590 Toyotomi Hideyoshi invaded the Kanto Plain. He laid siege to the powerful castle of Odawara and attacked the various castles of the Kanto. Hachioji Castle was one of the last. It was captured in a fierce battle on the 23rd of the 6th month (July 24). Odawara Castle surrendered less than two weeks later.

The castle was not rebuilt, but left as forested land, so the site has not disturbed and the original foundations remain. The residential site was excavated recently, and pillar bases and many pottery artefacts were found, and even some glass imported from Venice. The site has an information guidance center nearby, and many volunteer guides.