The Diocese of Tucson (Latin: Dioecesis Tucsonensis – Spanish: Diócesis de Tucson) is a Latin Church ecclesiastical territory – or diocese – of the Roman Catholic Church in southern Arizona in the United States. It is a suffragan diocese of the ecclesiastical province of the metropolitan Archdiocese of Santa Fe.

The mother church for the Diocese of Tucson is St. Augustine Cathedral in Tucson. Tucson is also home to Mission San Xavier del Bac. As of 2023, the bishop of Tucson is Edward Weisenburger.

The Diocese of Tucson is the fifth largest diocese in the continental United States. It comprises the following nine counties:

Gila, Graham, Greenlee, Pinal, Cochise, Santa Cruz, Pima, Yuma, and La Paz.

The Gila River Indian Community in Pinal County is not part of the diocese.

The first Catholic presence in southern Arizona was the Mission San José de Tumacácori near Nogales, founded in 1691. It was established by Reverend Eusebio Kino to minister to the Sobaipuri Native Americans, part of a string of missions he found in the northern desert regions of the Spanish Empire. The next year, Kion built the Mission San Xavier del Bac on the present-day San Xavier Indian Reservation.

The O'odham rebellion of 1751 forced the Mission San José de Tumacácori to move to its current location on the Santa Cruz River. During an Apache raid in 1771, the Mission San Xavier del Bac was destroyed. It was rebuilt by 1797 and is the oldest European structure in Arizona.

After the Mexican War of Independence ended in 1821, Mexico took control of the Southwest from Spain. The pastor of Mission San Xavier del Bac, Reverend Rafael Diaz, refused to sign a loyalty oath in 1828 to the new Mexican Government and was forced to leave the mission. The Mission San José de Tumacácori was abandoned by 1848 and was never used again as a mission.

With the 1854 Gadsden Purchase, southern Arizona became a part of the United States. In 1859, the Mission San Xavier del Bac, missing a priest since 1828, was taken over and staffed by the Diocese of Santa Fe.

In 1866, Bishop Jean-Baptiste Lamy of the Diocese of Santa Fe appointed Jean-Baptiste Salpointe as vicar general of Arizona. He was replacing Jesuit missionaries who had been recalled from the area. That same year, Salpointe arrived in Tucson with two other priests. At the time, Arizona consisted of approximately 6,000 settlers in some half a dozen settlements and several mining camps, as well as Native Americans inhabitants. Salpointe built new churches, organized new congregations, and founded schools and hospitals in the territory. Salpointe helped build San Agustin Church in Tucson, which would later become the first cathedral in the Arizona Territory.

Pope Pius IX established the Apostolic Vicariate of Arizona in 1868, taking its territory from the Diocese of Santa Fe. The pope named Salpointe as the first apostolic vicar. Salpointe left Arizona in 1885 to become coadjutor archbishop in Santa Fe. The second apostolic vicar of Tucson was Reverend Peter Bourgade, named by Pope Leo XIII in 1885.

Leo XIII converted the Apostolic Vicariate of Arizona into the Diocese of Tucson on May 8, 1897, covering the entire Arizona Territory along with parts of New Mexico and Texas. The pope named Bourgade as the first bishop of Tucson. During his two-year tenure as bishop, Bourgade established twelve schools and an orphanage and rebuilt the Cathedral of Saint Augustine. In 1899, Bourgade became archbishop of Santa Fe.

The second bishop of Tucson was Henry Regis Granjon, named by Leo XIII in 1900. During his tenure, the Mission San Xavier del Bac underwent needed restoration. In 1904, Granjon stated that his diocese included "...40,000 Catholics, 90,000 heretics and 30,000 infidels". In 1914, the Vatican erected the Diocese of El Paso, taking all the Texas counties from the Diocese of Tucson. Granjon died in 1922.

To replace Granjon, Pope Pius XI named Daniel Gercke of the Archdiocese of Philadelphia as the next bishop of Tucson in 1923. In 1939, Pope Pius XII established the Diocese of Gallup, taking all of the New Mexico territory from the Diocese of Tucson. Auxiliary Bishop Francis Joseph Green was named coadjutor bishop of Tucson by Pope John XXIII to assist Gercke in early 1960. When Gercke retired that year after 37 years as bishop of Tucson, Green automatically succeeded him.

Green began major restoration on St. Augustine's Cathedral in 1966, completing the effort in 1968. In 1969, the Vatican erected the Diocese of Phoenix, taking territory from the Diocese of Tucson. Green was instrumental in founding the Arizona Ecumenical Council, became an advocate of social justice, and provided ministries for African American, Native American and Hispanic Catholics. Green retired in 1981.

Pope John Paul II appointed Auxiliary Bishop Manuel Duran Moreno of Los Angeles as the next bishop of Tucson in 1982. In 2001, the pope named Auxiliary Bishop Gerald Frederick Kicanas of the Archdiocese of Chicago as coadjutor bishop in Tucson. After Moreno retired in 2003, Kicanas became the next bishop of Tucson. The Diocese of Tucson filed for Chapter 11 bankruptcy in September 2004, the second diocese to do so in US history. Kicanas retired in 2017.

Edward Weisenburger, formerly bishop of the Diocese of Salina, was named bishop of the Diocese of Tucson by Pope Francis in 2017. As of 2023, Weisenburger is the bishop of Tucson.

The Diocese of Tucson in 2005 reached an agreement in bankruptcy court to pay a $22.2 million settlement to victims of sex abuse by clergy. In 2013, Stephanie Innes of the Arizona Daily Star labeled the diocese as a "dumping ground" for abusive priests after it was revealed that several accused clergy from other diocese were sent to Tucson.

In 2018, Bishop Weisenburger stated that the diocese had fired ten employees over the past ten years due to charges of sexual misconduct against them. Commenting on the 2018 Pennsylvania grand jury report of sexual abuse by priests in that state, Weisenburger linked the so-called sexual revolution of the 1960s to these crimes: “It would be way too simplistic to blame a cultural movement for what individuals have done, but I also think it would be irresponsible to not acknowledge its role.”.

In December 2020, the Diocese of Tucson and the Archdiocese of Los Angeles were named in a federal racketeering lawsuit by two individuals alleging sexual abuse as minors by four priests in Arizona. One plaintiff, Diana Almader-Douglas, said that Reverend Charles Knapp sexually abused her when she was five years old at her home in Pirtleville in the 1970s. Weisenburger said the diocese immediately notified police of the allegation, which they declined to investigate. An outside investigation was unable to determine if the allegations were credible. A third individual joined the lawsuit in 2021.

1. Jean-Baptiste Salpointe (1868–1884), appointed Coadjutor Archbishop and later Archbishop of Santa Fe
2. Peter Bourgade (1885–1897)

1. Peter Bourgade (1897–1899), appointed Archbishop of Santa Fe
2. Henry Regis Granjon (1900–1922)
3. Daniel James Gercke (1923–1960)
4. Francis Joseph Green (1960–1981)
5. Manuel Duran Moreno (1982–2003)
6. Gerald Frederick Kicanas (2003–2017)
7. Edward Weisenburger (2017–present)

• Francis Joseph Green (1960)
• Gerald Frederick Kicanas (2001–2003)

Thomas Joseph O'Brien, appointed Bishop of Phoenix in 1981, resigned in 2003, convicted of felony of hit and run involving death, 2004.

The Diocese of Tucson as of 2023 had 15 elementary schools, two Pre-K through 12 schools, five high schools, and one early childhood center.

• Immaculate Heart High School – Oro Valley
• St. Augustine Catholic High School – Tucson
• Salpointe Catholic High School – Tucson
• San Miguel Cristo Rey High School – Tucson
• Yuma Catholic High School – Yuma

See List of parishes in the Roman Catholic Diocese of Tucson

• Roman Catholic Diocese of Tucson Official Site
• GigaCatholic with incumbent biography links
• Arizona Catholic Conference
• St. Gianna Oratory – Institute of Christ the King in Tucson Archived 2009-01-24 at the Wayback Machine

32°12′52″N 110°55′05″W / 32.21444°N 110.91806°W / 32.21444; -110.91806