In a land area of 9,140 square kilometers, the Daejeon diocesan territory includes Daejeon Metropolitan City and Chungcheongnam-do (province).
The diocese was erected as a "missio indepens" (independent mission) on May 8, 1948, and became an apostolic vicariate on June 23, 1958. On March 10, 1962, it was elevated to diocese and became a member of the ecclesiastical province headed by Seoul archdiocese. As of the end of 2004, it had 106 parishes, 218,082 Catholics and 237 priests.
Daejeon diocese is the birthplace of the first Korean priest, Saint Andrew Kim Tae-gon, and has many shrines connected with him such as the Solmoe Shrine. The diocese also has many historical places related to the persecutions of Christians in the 19th century, such as the Haemi Shrine and Galmaemot.
Daejeon diocese is concentrating on promoting priestly vocations and much work is done by the diocesan major seminary in this respect. About 20 priests are ordained annually as a result of the seminary's efforts.
The diocese also built the St. J. Hasang Education Center near Daejeon Catholic University for the education of lay people in the diocese and in the nation. The center was the venue of the 8th Plenary Assembly of the Federation of Asian Bishops' Conferences held in August 2004.
In Daejeon diocesan jurisdiction, the population is 3,818,000 at the end of 2016. (Some 7.0 percent of the whole population 51 million in the country) Most residents are ethnic Koreans.
Standard Korean is in use. English, a mandatory subject in schools, is spoken and understood in business and tourist areas. All traffic signs are in English and Korean.
Daejeon diocese falls within the temperate zone and has the four seasons of spring, summer, autumn and winter. The yearly average temperature is 11-13 degrees Celsius. The annual precipitation in the region averages 1,100-1,300 millimeters. Most of the rainfall occurs within the monsoon period of June through September.
The Chungcheongnam-do province is in the central area of the Korean peninsula. It is the lowest-lying region here with an average altitude of some 100 meters. The area is also the center of South Korea's railroads and highways. Daejeon is the junction of many highways and railways leading from Seoul to southeastern areas such as Daegu and Busan, and southwestern areas such as Gwangju and Mokpo.