The area of present-day Kagamiishi was part of ancient Mutsu Province and formed part of the holdings of Shirakawa Domain during the Edo period. After the Meiji Restoration, it was organized as part of Iwase District in the Nakadōri region of Iwashiro Province. Kagamiishi Village was formed on April 1, 1889 with the creation of the modern municipalities system. It was elevated to town status on August 1, 1962. During the 2011 Tohoku earthquake, over 1000 structures were severely damaged or destroyed, corresponding to approximately 23 percent of the town,