The Kasaoka area is part of ancient
Bitchū Province and numerous
shell middens from the
Jōmon period confirm that the area has been inhabited since prehistoric times. The place name 'Kasaoka' is said to have been derived from the area of influence of the 'Kasaomi clan' of the ancient
Kingdom of Kibi. Kasaoka Castle, was built by Murakami Takashige at the end of the
Muromachi period and was controlled by the
Mōri clan during the
Sengoku period. Under the Edo Period
Tokugawa shogunate, the area became part of the territory of the
Mizuno clan of
Fukuyama Domain. The Mizuno invested vast sums of money in
civil engineering projects to promote the development of new rice fields in Kasaoka, which originally had little flat land. However, the domain fell to attainder in the middle of the
Edo period, and the Kasaoka area was ruled as
tenryō territory about 170 years until the end of the Edo period. Following the
Meiji restoration, the village of Kasaoka was established within
Oda District, Okayama with the creation of the modern municipalities system on June 1, 1889. It was raised to town status on October 23, 1891 and to city status on April 1, 1952. Due to its strong historical, cultural and economic ties with Fukuyama, proposals have been made for a merger between the two municipalities. ==Government==