Miyagi Prefecture was formerly part of the province of Mutsu. Mutsu Province, on northern Honshu, was one of the last provinces to be formed as land was taken from the indigenous Emishi, and became the largest as it expanded northward. The ancient capital was at Taga-jō in modern Miyagi Prefecture.

In the third month of second year of the Wadō era (709), there was an uprising against governmental authority in Mutsu Province and in nearby Echigo Province. Troops were promptly dispatched to subdue the revolt.

In Wadō 5 (712), the land of Mutsu Province was administratively separated from Dewa Province. Empress Gemmei's Daijō-kan continued to organize other cadastral changes in the provincial map of the Nara period, as in the following year when Mimasaka Province was divided from Bizen Province; Hyūga Province was sundered from Osumi Province; and Tamba Province was severed from Tango Province.

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