[2] The French missionary Claude-Jean Allouez was stationed at Kaskaskia, Illinois, for eight weeks from June to August 1673 before returning to St. Francis Xavier Mission near De Pere, Wisconsin.

[4] At that time, the Catholics of Cahokia and the surrounding territory, including the city of St. Louis across the river, were attended to by Father De Saintpierre.

The organization of the congregation of Prairie du Rocher, Illinois coincides with the building of the first Fort de Chartres on the Mississippi River in 1720.

After the American Revolution ended in 1783, Pope Pius VI erected in 1784 the Prefecture Apostolic of the United States, encompassing the entire territory of the new nation.

The earliest parishes in the region were the Irish St. Patrick's in Ruma in 1818, the French St. Francis in St. Francisville in 1818 and the English St. Augustine of Canterbury in Hecker in 1824.

[13] In 1903, at Janssen's request, the Poor Handmaids of Christ religious order set up a hospital in East St. Louis, Illinois.

He also provided facilities for Black Power activists looking to challenge racial discrimination in that city, including Charles Koen and his United Front organization.

[18] Zuroweste came under pressure from White Cairo residents to recall Montroy, but gave him qualified support after demands from progressive Catholic organizations.

[20] When Zuroweste retired in 1977, Pope Paul VI named Auxiliary Bishop William Cosgrove of the Diocese of Cleveland.

John Paul II then appointed James Patrick Keleher of the Archdiocese of Chicago as the new bishop of Belleville.

In July 2022, McGovern announced the planned sale of the diocesan bishop's residence and his move to a more modest space in the Cathedral of St. Peter rectory.

The money from the sale, he announced, would be used to subsidize various ministries and charities, including the establishment of a fund benefiting expectant mothers and children.

[22] During the course of 1993, Bishop Keleher removed seven priests and one deacon with credible accusations of sexual abuse of minors from ministry in the diocese.

In 1973, Gina Parks, a 16-year-old parishioner in St. Francisville, told diocesan officials that her parish priest, Raymond Kownacki, had raped and impregnated her.

By 1982, allegations surfaced that Kownacki was sexually abusing young boys at St. Theresa, in particular 12 year old James Wisniewski.

[26] An Illinois man known as J. Christ sued the diocese for $100,000 in 2014, saying that he was sexually abused in the summers of 1970 and 1971 by Robert J. Vonnahmen at Camp Ondessonk in Ozark.

[30] In October 2020, Bishop McGovern removed Anthony Onyango from his position as administrator for two parishes, citing an allegation of verbal misconduct with a minor.

[33][34] Stanley Girard Schlarman (1979-1983), appointed Bishop of Dodge City Joseph Henry Leo Schlarman, appointed Bishop of Peoria in 1930 and subsequently named archbishop ad personam Media related to Roman Catholic Diocese of Belleville at Wikimedia Commons