The foundation of the Iwakiyama Shrine predates the historical period, and Mount Iwaki was a holy mountain for the local Emishi tribes. Per shrine tradition, the shrine was established on the summit of Mount Iwaki in the year 780. It was rebuilt by the folk-hero Sakanoue no Tamuramaro in the year 800 and dedicated to his father Sakanoue no Karitamaro. Several subsidiary shrines were built around the base of the mountain in an area called the by the local inhabitants. One of these subsidiary shrines to the southeast of the mountain developed into the Shingon sect Buddhist temple of in 1091, and became the predecessor of the present shrine. The three main peaks on Mount Iwaki were identified with the Buddhist deities of Amida Nyorai, Yakushi Nyorai and Kannon Bosatsu.