Kōza District was one of the ancient subdivisions of Sagami Province, extending from Sagami Bay north to the border of Musashi Province between the Sagami River and the Sakai River. It was mentioned in the Nihon Shoki records of 675 AD in the Nara period as Takakura District (高倉郡, Takakura-gun). The provincial capital of Sagami Province and its kokubunji were located within Kōza District, although its exact location is today unknown.
After the Meiji Restoration, it was established as a district under the cadastral reform of 1878, with a district office built near what is now part of Chigasaki. This was moved to Fujisawa-Ōsaka Town (present-day Fujisawa) in 1906.
On April 1, 1889, Kōza District was divided into one town (Fujisawa-Ōsaka) and 22 villages. In 1908, Chigasaki Village became a town, as did Kamimizo in 1928, and Zama in 1937. Fujisawa became a city in 1940. Samukawa and Ebina became towns the same year. In 1941, Zama, Kamimizo and six neighboring villages merged to form the town of Sagamihara. Yamato became a town in 1943, Shibuya in 1944 and Ayase in 1945. Chigasaki became a city in 1947.
In 1948, Zama was separated from Sagamihara, which became a city in 1954.
The town of Shibuya dissolved in 1955, with the southern portions merging with Fujisawa, and the northern portion reverting to the status of village until absorbed by Yamato town in 1956. Yamato became a city in 1959, and both Ebina and Zama became cities in 1971, and Ayase in 1978, leaving Samukawa as the only remaining component of Kōza District.
