Sōja is a city located in Okayama Prefecture, Japan. As of 31 March 2023, the city had an estimated population of 69,428 and a population density of 330 persons per km². The total area of the city is 211.90 square kilometres (81.82 sq mi).

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.