The prefecture has some archaeological sites going back to the Jōmon period (around 400 BCE). About 3,000 years ago, Mount Hakone produced a volcanic explosion which resulted in Lake Ashi on the western area of the prefecture.
It is believedYamato dynasty ruled this area from the 5th century onwards. In the ancient era, its plains were very sparsely inhabited.
In medieval Japan, Kanagawa was part of the provinces of Sagami and Musashi. Kamakura in central Sagami was the capital of Japan during the Kamakura period (1185–1333).
During the Edo period, the western part of Sagami Province was governed by the daimyō of Odawara Castle, while the eastern part was directly governed by the Tokugawa shogunate in Edo (modern-day Tokyo).
Commodore Matthew Perry landed in Kanagawa in 1853 and 1854 and signed the Convention of Kanagawa to force open Japanese ports to the United States. Yokohama, the largest deep-water port in Tokyo Bay, was opened to foreign traders in 1859 after several more years of foreign pressure, and eventually developed into the largest trading port in Japan. Nearby Yokosuka, closer to the mouth of Tokyo Bay, developed as a naval port and now serves as headquarters for the U.S. 7th Fleet and the fleet operations of the Japan Maritime Self-Defense Force. After the Meiji period, many foreigners lived in Yokohama City, and visited Hakone. The Meiji government developed the first railways in Japan, from Shinbashi (in Tokyo) to Yokohama in 1872.
The epicenter of the 1923 Great Kanto earthquake was deep beneath Izu Ōshima Island in Sagami Bay. It devastated Tokyo, the port city of Yokohama, surrounding prefectures of Chiba, Kanagawa, and Shizuoka, and caused widespread damage throughout the Kantō region. The sea receded as much as 400 metres from the shore at Manazuru Point, and then rushed back towards the shore in a great wall of water which swamped Mitsuishi-shima. At Kamakura, the total death toll from earthquake, tsunami, and fire exceeded 2,000 victims. At Odawara, ninety percent of the buildings collapsed immediately, and subsequent fires burned the rubble along with anything else left standing.
Yokohama, Kawasaki and other major cities were heavily damaged by the U.S. bombing in 1945. Casualties amounted to more than several thousand. After the war, General Douglas MacArthur, the Supreme Commander of the Allied Powers for the Occupation of Japan, landed in Kanagawa, before moving to other areas. U.S. military bases still remain in Kanagawa, including Camp Zama (Army), Yokosuka Naval Base, Naval Air Station Atsugi (Navy).
In 1945, Kanagawa was the 15th most populous prefecture in Japan, with the population of about 1.9 million. In the years after the war, the prefecture underwent rapid urbanization as a part of the Greater Tokyo Area. The population as of September 1, 2014, is estimated to be 9.1 million. Kanagawa became the second most populous prefecture in 2006.