Mutsu Bay
Hiranai occupies the Natsudomari Peninsula, the northern end of the Ōu Mountain Range that juts into central Mutsu Bay. The town's population is concentrated near the Japan National Route 4 passing through the east and west of the town and the Aoimori Railway Line (formerly the Tōhoku Main Line). The town office is in the settlement of Kominato, the central part of Hiranai centered around the valley of the Kominato River. The Kominato River begins in the mountains in the south of Hiranai, and flows north through the mountains until it reaches the flat land the town is situated on. After passing through Kominato, it joins the Morita River, which empties into Mutsu Bay shortly after their confluence. The southern part of Hiranai is mainly mountainous. The edges of the town make up the bulk of the Asamushi-Natsudomari Prefectural Natural Park.