Akaoka was raised to town status on February 15, 1899, followed by Noichi on February 1, 1926, Yasu on January 1, 1943 and  Kagami on April1, 1955. The city of Kōnan was created by the merger of these four towns and the village of Yoshikawa on March 1, 2006.
Akaoka was upgraded to town status on February 15, 1899, followed by Noichi on February 1, 1926, Yasu on January 1, 1943 and Kagami on April 1, 1955. The resulting towns were later merged with the village of Yoshikawa to form the city of Kōnan on March 1, 2006.