PITTSBURGH, Diocese of. - City and diocese in the State of Pennsylvania, U.S.A. The diocese of P., a suffragan of Philadelphia, today covers a territory of 7,238 square miles; it has a total population (1950 census) of 2,799,675 inhabitants, of whom 832,745 are Catholics (1951). There are 1,020 priests, of whom 262 are religious of 9 different congregations, 416 parishes, 267 chapels, 65 missions, 44 female congregations with 4,612 religious, 4 colleges and universities (Duquesne University, directed by the Fathers of the Holy Spirit), 4 orphanages, 10 hospitals and 5 homes for the aged.
It is very likely that the Jesuit Bonnecamp held the first religious service for the whites of the diocese in 1749. The city of P. was so named to honor William Pitt, prime minister of England, when the British army took possession of Fort Duquesne in 1758, afterward called Fort Pitt or P. Since the French had left the territory, the Catholic religion had almost no adherents in western Pennsylvania for about 30 years, and the Catholics who settled there were opposed by the Calvinists.
The first church of P., still known today under the name of "Old St. Patrick's," was opened in Aug. 1811. As early as 1825, Msgr. Benedict Joseph Flaget considered P. as the seat of a future diocese, but only in 1836 did Msgr. Francis P. Kenrick propose the dismemberment of the diocese of Philadelphia. In Jan. 1836, the Rev. John Hughes was appointed bishop of the new see of P., but shortly afterward Rome annulled the appointment. On May 14, 1843, with the dismemberment of Philadelphia, the erection of the diocese of P. was again proposed to the Holy See by the V Provincial Council of Baltimore. With the brief Universi Dominici gregis Gregory XVI erected P. for the western part of Pennsylvania (Aug. 8, 1843); Msgr. Michael O'Connor was the first bishop, consecrated in Rome on Aug. 15, and he took possession on Dec. 3 of the same year. After great activity in the diocese he entered the Society of Jesus; he founded a diocesan seminary and called the Oblates of Mary Immaculate from Canada to direct it, but it was for only a short time. In 1852 the diocese was so prosperous that its dismemberment was considered. The I Plenary Council of Baltimore, meeting on May 9, 1852, made the proposal to Rome. Indeed, on July 29, 1852, the diocese of Erie was erected. P. was then reduced to 11,314 square miles. Under Msgr. M. Domenec, successor of Msgr. O'Connor, the diocese was again dismembered to form the diocese of Allegheny City, but only for a short time, because that see was suppressed. In 1901 the Holy See erected the diocese of Altoona by dismemberment of P. and of Harrisburg.