It comprises the following nine counties: Gila, Graham, Greenlee, Pinal, Cochise, Santa Cruz, Pima, Yuma, and La Paz.

The first Catholic presence in southern Arizona was the Mission San José de Tumacácori near Nogales, founded in 1691.

[1] 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.

[2] The O'odham rebellion of 1751 forced the Mission San José de Tumacácori to move to its current location on the Santa Cruz River.

[6] 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.

[7] Pope Pius IX established the Apostolic Vicariate of Arizona in 1868, taking its territory from the Diocese of Santa Fe.

[8][10] During his two-year tenure as bishop, Bourgade established twelve schools and an orphanage and rebuilt the Cathedral of Saint Augustine.

To replace Granjon, Pope Pius XI named Daniel Gercke of the Archdiocese of Philadelphia as the next bishop of Tucson in 1923.

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.

[23] 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.

[24][25][26][27] Thomas Joseph O'Brien, appointed Bishop of Phoenix in 1981, resigned in 2003, convicted of felony of hit and run involving death, 2004.