The Diocese of Peoria comprises the following Illinois counties: Bureau, Champaign, DeWitt, Fulton, Hancock, Henderson, Henry, Knox, LaSalle, Livingston, Logan, Marshall, Mason, McDonough, McLean, Mercer, Peoria, Piatt, Putnam, Rock Island, Schuyler, Stark, Tazewell, Vermilion, Warren and Woodford.

Mass was celebrated there by three French Recollect Fathers: Gabriel Ribourdi, Zenobius Membre, and Louis Hennepin.

With some breaks in the succession, the line of missionaries extends to within a short period of the founding of modern Peoria.

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.

[4] In 1839, Father Raho, an Italian priest, visited Peoria, remaining long enough to build the old stone church in Kickapoo.

Many of the early Irish immigrants in Illinois in the mid-1800s came to work on the Illinois and Michigan Canal Owing to the failure of the contracting company, the workers received their pay in land scrip instead of cash, forcing them to settle on virgin farm land.

Pius IX appointed John Spalding of the Diocese of Louisville as the first bishop of Peoria in 1876.

During the early 1920s, the future Archbishop Fulton Sheen, a popular television host in the 1950s, was a priest in the diocese.

After Sheen spent time in pastoral and teaching jobs in the United Kingdom, Dunne ordered him to return to Peoria in 1925.

However, instead of allowing Sheen to take one of these prestigious positions, Dunne assigned him as a curate to St. Patrick's, a poor parish in Peoria.

O'Rourke sold the episcopal residence on Glen Oak Avenue and moved to a one-bedroom brick ranch house near St. Mary's Cathedral, donating the money to the diocesan fund for retired priests.

While bishop, Myers issued an order forbidding Catholic hospitals in the diocese from providing emergency contraception to rape victims, a restriction he later eased.

[12] He also fired a teacher at a Catholic high school for inviting a speaker to discuss the ordination of women to the priesthood.

[12] During Myers' tenure, the diocese saw a rapid increase in vocations to the priesthood, with many seminarians being drawn to his more conservative theology.

However, in 2014, citing undocumented verbal agreements, Jenky announced that he would not permit the cause to progress until Sheen's remains were transferred to Peoria from St. Patrick's Cathedral in New York City.

[14][15] After three years of litigation between the diocese and the Archdiocese of New York regarding Sheen's wishes, the court ordered his remains to go to Peoria, where they arrived in June 2019.

[16] On May 11, 2020, Pope Francis named Louis Tylka of the Archdiocese of Chicago as coadjutor bishop of the diocese.

[17] The lawsuit claimed that Bishop Myers allowed Maloney to remain in ministry, despite evidence of prior sexual abuse.

In 1969, production and printing of the paper were moved within the diocese and the name was changed to The Catholic Post.