The Diocese of Bismarck (Latin: Dioecesis Bismarckiensis) is a Latin Church ecclesiastical territory, or diocese, of the Catholic Church in western North Dakota in the United States. It is a suffragan diocese of the metropolitan Archdiocese of Saint Paul and Minneapolis. The bishop is David Kagan. The mother church of the diocese is Cathedral of the Holy Spirit.

The Diocese of Bismarck encompasses 24 North Dakota counties over 34,000 square miles. It has a total population over 253,000 people, with approximately 66,400 Catholic church members.

The Dakotas area went through several Catholic jurisdictions before the creation of the Diocese of Fargo:

• Diocese of Saint Louis (1826 to 1837)
• Diocese of Dubuque (1837 to 1850)
• Diocese of Saint Paul (1850 to 1879)
• Vicariate Apostolic of Dakota (1879 to 1889)
• Diocese of Jamestown (later Fargo) (1889 to 1909)

The first Catholic church in western North Dakota was the Church of the Immaculate Conception, dedicated in Bismarck in 1875.

On December 31, 1909 Pope Pius X established the Diocese of Bismarck, taking its territory from the Diocese of Fargo. He appointed Reverend Vincent de Paul Wehrle as the first bishop of the new diocese. During Wehrle's 29-year-long tenure, the Catholic population increased from 25,000 to 55,000. He constructed 55 churches, 18 parochial schools, and four hospitals were established. Wehrle established 115 new congregations. He also began construction on the Cathedral of the Holy Spirit, but was forced to abandon his efforts due to the Great Depression.

After Wehrle retired in 1939, Pope Pius XII named Monsignor Vincent Ryan of Fargo as the second bishop of Bismarck. During his 11-year tenure, Ryan constructed 69 church buildings for a total cost of over ten million dollars. Ryan founded the diocesan newspaper, Dakota Catholic Action, in 1941. The Cathedral of the Holy Spirit was dedicated in 1945. Ryan publicly opposed the 1948 North Dakota "anti-garb" law, which prohibited nuns from wearing their religious habits while teaching in public schools. Ryan died in 1951.

In 1952, Lambert Hoch of the Diocese of Sioux Falls was appointed the third bishop of Bismarck, by Pius XII. During his four-year tenure, Hoch worked to promote vocations to the priesthood and religious life; between 1952 and 1960, 29 priests were ordained for the diocese and 13 for Assumption Abbey in Richardton. Hoch became bishop of Sioux Falls in 1956.

Pius XII named Hilary Hacker of Saint Paul as the fourth bishop of Bismarck in 1956. Hacker dedicated much of his tenure implementing the Second Vatican Council reforms, especially the Mass of Paul VI, and greater participation of the laity. His tenure was also marked by high Catholic school enrollment, as well as the founding of Bishop Ryan High School in Minot and Trinity High School in Dickinson. He also established an annual appeal called God's Share; between 1956 and 1963, the annual collection rose from $165,000 to $225,000. Hacker retired in 1982.

The next bishop of Bismarck was Auxiliary Bishop John Kinney of Saint Paul and Minneapolis, named by Pope John Paul II in 1982. Kinney became bishop of the Diocese of Saint Cloud in 1995. To replace Kinney, the pope appointed Auxiliary Bishop Paul Zipfel of the Archdiocese of Saint Louis in 1997 as bishop of Bismarck. Zipfel retired in 2011.

The bishop of Bismarck, as of 2023, is David Kagan from the Diocese of Rockford. He was appointed by Pope Benedict XVI in 2011. In 2015, Kagan announced that the diocese was cutting ties with the Boy Scouts of America due to policy changes allowing gay men to become scout leaders and volunteers.

Kagan announced in 2022 that the diocese would investigate the life of Michelle Duppong for possible canonization. She conducted missionary work for several years at universities and colleges in North Dakota.

In 2002, Bishop Zipfel introduced a zero-tolerance policy of sexual abuse allegations against priests in the diocese. Under the policy, anyone accused of abuse would be immediately removed from active ministry and reported to the police for investigation.

In 2019, the diocese released the names of 22 clergy with credible accusations of sexual abuse of minors since 1950. In 2020, Bishop Kagan released a list of 18 diocesan clergy and four extern clergy with credible accusations of sexual abuse of minors. He stated that the last substantiated case of sexual abuse occurred in 1989.

1. John Baptist Vincent de Paul Wehrle, O.S.B. (1910–1939)
2. Vincent James Ryan (1940–1951)
3. Lambert Anthony Hoch (1952–1956), appointed Bishop of Sioux Falls
4. Hilary Baumann Hacker (1956–1982)
5. John Francis Kinney (1982–1995), appointed Bishop of Saint Cloud
6. Paul Albert Zipfel (1996–2011)
7. David D. Kagan (2011–Present)

• Sylvester William Treinen, appointed Bishop of Boise City in 1962
• Austin Anthony Vetter, appointed Bishop of Helena in 2019

The Diocese of Bismarck has three high schools and 11 elementary schools or pre-schools.

• Bishop Ryan High School – Minot
• St. Mary's Central High School – Bismarck
• Trinity High School – Dickinson

• Roman Catholic Diocese of Bismarck
• Roman Catholic Diocese of Bismarck Official Site-archives

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