At the end of the 19th century, there were three districts (), seven towns (), and 51 villages (). During the 20th century, a series of mergers steadily reduced the number of political local authorities, following the recent trend in Japan to cut the costs of having separately run local administrations. The current city () covering the whole island was established on March 1, 2004 from a merger of all remaining municipalities on the island: the city of Ryōtsu: the towns of Aikawa, Kanai, Sawata, Hatano, Mano, Hamochi and Ogi; and the villages of Niibo, and Akadomari (all from Sado District).