The area of Tosu was part of ancient
Hizen Province, and during the
Edo period was an exclave of
Tsushima-Fuchū Domain under the
Tokugawa shogunate. Tashiro-juku was home to the taxation rice storehouse and magistrate's office of the domain. It was also a stopping place for
Joseon missions to Japan. The
Sō clan prospered from its knowledge of
Chinese traditional medicine and access to supplies imported from Korea, and the region was considered one of the four major pharmaceutical centers in pre-modern Japan. Following the
Meiji restoration, the area was the center of the 1874
Saga Rebellion, and a battle between the government troops and the rebel army occurred on Mount Asahi. The villages Asahi, Fumoto, Kizato, Tashiro and Todoroki were created on April 1, 1889 with the establishment of the modern municipalities system. Todoroki was elevated to town status on March 19, 1907 and renamed Tosu. Tashiro was elevated to town status on March 11, 1936. On April 1, 1954 Tosu merged with Tashiro and the villages of Asahi, Fumoto and Kizato and was raised to city status. ==Government==