Shiroishi Castle was a Japanese castle (flatland castle) located in Shiroishi City, Miyagi Prefecture (Shiroishi, Katta County, Mutsu Province). It is also known as Masuoka Castle (Masuoka). The castle is a designated historic site by Shiroishi City. It is said to have been the residence of the Shiroishi clan (Karita clan) during the Middle Ages. The lord of the castle changed several times towards the end of the Sengoku period, and in the Edo period it became the castle of the Katakura clan, vassals of the Sendai domain. Along with Yatsushiro Castle in Kyushu, it was not subject to the Edo Shogunate's one castle per province rule, and continued to exist until the Meiji Restoration.