Sodegaura is mentioned in the Nara period chronicle Kojiki in connection with the Yamatotakeru mythology, and at that time applied to the entire western coastline of the Boso Peninsula. Modern Sodegaura was part of Kimitsu District from the Meiji period. Sodegaura Town was formed on March 31, 1955 from the merger of the town of Shōwa with the neighboring village of Nagaura and a portion of the village of Negata. It expanded through merger with the town of Hirakawa on November 3, 1971. On April 1, 1991 it was elevated to city status.