Hachimantai is located in the Ōu Mountains of far northwest Iwate Prefecture, bordered by Aomori Prefecture to the north and Akita Prefecture to the west. The headwaters of the Yoneshiro River are in Hachimanai. Part of Mount Hachimantai and Mount Iwate are within its borders. Parts of the city are within the borders of the Towada-Hachimantai National Park. Mount Iwate, the highest mountain in Iwate Prefecture, is on the border of Hachimantai with Shizukuishi and Takizawa.