Mutsu Bay is a bay located within Aomori Prefecture, in the northern Tōhoku region of northern Japan. It has an east-west distance of approximately 40 kilometers and a north-south distance of approximately 40 kilometers at its eastern end, with a total area of approximately 1,667.89 square kilometers.

Aomori Prefecture ([a̠o̞mo̞ɾʲikẽ̞ɴ]) is a prefecture of Japan in the Tōhoku region. The prefecture's capital, largest city, and namesake is the city of Aomori. Aomori is the northernmost prefecture on Japan's main island, Honshu, and is bordered by the Pacific Ocean to the east, Iwate Prefecture to the southeast, Akita Prefecture to the southwest, the Sea of Japan to the west, and Hokkaido across the Tsugaru Strait to the north. Aomori Prefecture is the 8th-largest prefecture, with an area of 9,645.64 km2 (3,724.20 sq mi), and the 31st-most populous prefecture, with more than 1.18 million people. Approximately 45 percent of Aomori Prefecture's residents live in its two core cities, Aomori and Hachinohe, which lie on coastal plains. The majority of the prefecture is covered in forested mountain ranges, with population centers occupying valleys and plains. Aomori is the third-most populous prefecture in the Tōhoku region, after Miyagi Prefecture and Fukushima Prefecture. Mount Iwaki, an active stratovolcano, is the prefecture's highest point, at almost 1,624.7 m (5,330 ft).