The Catholic Diocese of Daejeon (천주교 대전교구,Cheonjugyo Daejeon Gyogu) was established on May 8, 1948, when it was separated from the Apostolic Vicariate of Gyeongseong, today the Archdiocese of Seoul. The diocese oversees all of Chungcheongnam-do, all of Daejeon Metropolitan City, and most of Sejong Special Self-Governing City (excluding Bugang-myeon). At the time of its establishment, it had 13 parishes, 19 priests (1 bishop and18 priests), and about 18,000 faithful. The first bishop, Bishop Adriano Won Hyeong-geun, laid the foundation of the diocese by providing relief supplies, operating orphanages, and supporting education in the difficult years following the Korean War.

The fourth bishop, Bishop Lazarus You Heung-sik, opened the “Daejeon Catholic Agricultural and Fisheries Support Center” to assist neighbors in need and launched Korea’s first “mobile food market” to promote a culture of sharing in the region. He also initiated the “One-Hundred-Won Meal Sharing Movement” to encourage remembering the poor at every meal, welcomed Pope Francis’ visit to the diocese during the 6th Asian Youth Day, and convened a diocesan synod for the renewal of the diocesan community. Archbishop Lazarus You Heung-sik was appointed Prefect of the Dicastery for the Clergy on June 11, 2021.

As of 2019, the Diocese of Daejeon, responsible for Daejeon Metropolitan City, Chungcheongnam-do, and Sejong Special Self-Governing City, has grown to 142 parishes, 383 priests (3 bishops and 380 priests), and about 330,000 faithful.

In Bango-dong, Sejong City, the Diocese of Daejeon purchased land in March 2016 and completed the construction of its new diocesan complex in April 2019. Most diocesan departments formerly located at the old diocesan office in Yongjeon-dong, Daejeon, have now relocated. The large building visible from the entrance of the diocesan complex is St. John Paul II Church.

The diocesan complex consists of the main administrative building Daegon Hall, the priests’ residence Yang-eop Hall, the bishop’s residence Dablé Hall, an open courtyard, Daegon Square, the priests’ courtyard, and St. John Paul II Church. Daegon Square, located directly in front of Daegon Hall, is named in honor of St. Andrew Kim Dae-geon. A statue of Our Lady stands to one side, and the entire area offers a quiet, peaceful atmosphere.