Satomi clan
Ichinomiya Castle was a mountain-top fortification built by the Satomi clan, rulers of most of the Bōsō Peninsula during the Sengoku period as protection for their northern holdings in eastern Kazusa Province. Following the Battle of Odawara in 1590, the Kantō region was assigned to Tokugawa Ieyasu by the warlord Toyotomi Hideyoshi, who also restricted the Satomi to Awa Province for their lukewarm support of his campaigns against the Later Hōjō clan. Tokugawa Ieyasu appointed Honda Tadakatsu, one of his hereditary retainers, to be "daimyō" of the new 100,000 "koku" Ōtaki Domain, and the old fortifications at Ichinomiya were abandoned.