Mimasaka Province was a province of Japan in the area that is northern Okayama Prefecture in the Chūgoku region of western Japan. Mimasaka bordered Bitchū, Bizen, Harima, Hōki, and Inaba Provinces. Its abbreviated form name was Sakushū (作州). In terms of the Gokishichidō system, Mimasaka was one of the provinces of the San'in circuit. Under the Engishiki classification system, Mimasaka was ranked as one of the 35 "superior countries" (上国) in terms of importance, and one of the "near countries" (近国) in terms of distance from the capital. The provincial capital was located in what is now the city of Tsuyama.

Okayama Prefecture is a prefecture of Japan located in the Chūgoku region of Honshu. Okayama Prefecture has a population of 1,906,464 and has a geographic area of 7,114 km2. Okayama Prefecture borders Tottori Prefecture to the north, Hyōgo Prefecture to the east, and Hiroshima Prefecture to the west.