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 promoted to town status in 1899, followed by Noichi in 1926, Yasu in 1943, and Kagami in 1955. These towns eventually merged with the village of Yoshikawa to create the city of Kōnan on March 1, 2006.