Onagawa is a town located in Miyagi Prefecture, Japan. As of 30 April 2020, the town had an estimated population of 6,319, and a population density of 97 persons per km2 in 3,110 households. The total area of the town is 65.35 square kilometres (25.23 sq mi).

Miyagi Prefecture is a prefecture of Japan located in the Tōhoku region of Honshu. Miyagi Prefecture has a population of 2,265,724 and has a geographic area of 7,282 km2 (2,812 sq mi). Miyagi Prefecture borders Iwate Prefecture to the north, Akita Prefecture to the northwest, Yamagata Prefecture to the west, and Fukushima Prefecture to the south.