In a land area of 27,051 square kilometers, the diocesan territory covers Kanagawa, Shizuoka, Nagano and Yamanashi prefectures.
In the diocesan territory, the population is 15,750,398 at end of 2017. Most residents are ethnic Japanese. There are also 335,289 non-Japanese people, according to the Immigration Bureau of Japan.
The territory also has many languages/dialects.
The diocese of Yokohama was established on Nov. 9, 1937, when the archdiocese of Tokyo was given over to the care of Japanese clergy, and the eight prefectures of Kanagawa, Shizuoka, Yamanashi, Nagano, Saitama, Gumma, Tochigi, and Ibaraki were entrusted to the Paris Foreign Mission Society.
On Nov. 9, 1939, the prefecture apostolic of Urawa was established and the four prefectures of Saitama, Gumma, Tochigi, and Ibaraki were entrusted to the Canadian Franciscans.
At the time of the establishment of the diocese of Yokohama, Archbishop Jean-Baptiste-Alexis Chambon, M.E.P., who had been archbishop of Tokyo, served as the first ordinary. When he retired in 1941, Monsignor Miyoichi Ideguchi, and then, from 1944, Monsignor Tatewaki Toda served as administrator apostolic of the diocese of Yokohama. With the death of Monsignor Toda, Archbishop Doi of Tokyo served temporarily at the same time as ordinary of the diocese of Yokohama. However, in 1947 Father Asagoro Wakita was consecrated and took over as bishop of Yokohama. In 1951 Bishop Wakita resigned, and Father Katsusaburo Arai was appointed bishop of Yokohama. He was consecrated bishop on Feb. 24, 1952, and retired in 1979.
On Oct. 30, 1979, Bishop Fumio Hamao, auxiliary bishop of Tokyo, was appointed bishop of Yokohama. He was installed on Jan. 15, 1980.
On June 15, 1998, Pope John Paul II nominated Bishop Hamao as president of the Pontifical Council for the Pastoral Care of Migrants and Itinerant Peoples at the Vatican. With this appointment, effective June 15, 1998, Bishop Hamao became an archbishop and relinquished the office of bishop of Yokohama. He was succeeded by Father Masahiro Umemura, who was appointed March 16, 1999, and was ordained bishop on May 15 that year. (Catholic Bishops' Conference of Japan, 2010)
Airplanes, railways, ships and buses are in use in the diocesan territory.
Throughout Japan, literacy is 99 percent, according to Central Intelligence Agency, USA, in 2010.