Kasaoka City municipalized through the incorporation of Imai-son in April 1, 1951 and Kanaura-cho in April 1, 1952.
On October 1, 1953, 6 more villages, Shiromi, Suyama, Oi, Yoshida Niiyama, Konoshimauchi, were incorporated. On April 1, 1955, 5 villages: Konoshimasoto-cho, Shiraishijima-son, Kitagishima-cho, Manabeshima-son, Oshima-son were incorporated. Thereafter, the City area expanded to 117.9k, with 73,552 inhabitants and 16,604 households after the incorporation of Kitagawa-son on April 1, 1960 and as a result it became a mid sized city. Thanks to the mild weather and superb views, Kasaoka City has advanced rapidly in the fields of tourism, economy, industry, and culture.
Kasaoka City was designated as the Bingo special industrial development area in 1965. The governmentﾐrun, Kasaoka Bay reclaiming project started in 1966. At a great cost, 30 billion yen, 1,191ha of land were created and in March 2000 the Bay Farm Kasaoka was completed as a large-scale farm. In one portion of this new large-scale farm the first road being used for a takeoff and landing facility for aircraft in Japan was accomplished in October 1991. Since that time aqricultural products is being distributed by using aircraft.
Moreover, including land readjustment, public sewers and the development of highways have been progressing steadily to this create 21st century city.