The Tsukuriyama Kofun, the 10th largest burial mound in Japan, and the mountain-fortress of Ki Castle are among the many surviving relics of that period.

The area prospered in the Muromachi period onwards as a "temple town" at the gates of the Bitchū-no-kuni Sōja-gū from which it derives its name.

Following the Meiji restoration, the village of Sōja was established with the creation of the modern municipalities system on April 1, 1889 and was raised to town status on February 26, 1896.

Sōja has a mayor-council form of government with a directly elected mayor and a unicameral city council of 22 members.

In terms of national politics, the city is part of the Okayama 3rd district of the lower house of the Diet of Japan.

Production of automobile parts dominates the local industry, although food processing is also important.