It is probable that the first priest to visit this region was Father Joseph de Bonnecamps, Jesuit missionary and cartographer.
He was a member of the expedition of Celoron de Bienville which in 1749 explored the Ohio and Allegheny Rivers in the interest of French claims; he conducted services near or possibly within the limits of the present city.
In 1754 a fort on the site of Pittsburgh. was captured by the French, rebuilt, and named Fort Duquesne, and the chapel within the stockade was dedicated in honor of the Assumption of the Blessed Virgin of the Beautiful River.
The chaplain was Friar Denys Baron, a Recollect priest; he and the chaplains of two other forts kept a record of baptisms and burials in this region from 1753 to 1756, and this register contains the names of some Indian converts.
For some time, after the British took the fort and named it Fort Pitt, there were few Catholics in the region.
In 1784 a group of Catholic families sent a messenger to Baltimore requesting that a priest be sent to them once or twice a year, and in the next few years several pioneer priests from various places visited them at irregular intervals.
The first resident pastor, Father William Francis Xavier O'Brien, came from Baltimore, where he had just been ordained, 1808, and founded Saint Patrick's Church; in less than three years the church was dedicated and Confirmation administered there by Bishop Egan of Philadelphia.
The next church, Saint Paul's, was nearly finished by Father O'Brien's successor, Father Charles B. Maguire.
In 1834 it was estimated that the population of the city, about 20,000, included four or five thousand Catholics.
The next year a Catholic school was established and in 1838 an orphan asylum.
In 1839 the Redemptorists, the first community of men in Pittsburgh, undertook the care of the German-speaking residents of the city, for whom they founded the Church of Saint Philomena.
The Diocese of Pittsburgh was established in 1843 under Bishop Michael O'Connor, who had already been pastor of Saint Paul's and had established a parish school, a men's literary society, and a reading room.
As bishop he introduced religious communities of men and of women and established several parishes and institutions and a chapel for local blacks.
Under his direction the weekly Pittsburgh Catholic was founded in 1844.
In 1843 the Sisters of Mercy made at Pittsburgh their first foundation in the United States.
The rapid industrial growth of the city during the 19th century brought a great increase in the number of Catholics of many nationalities, necessitating for some time the use in the churches of ten or more languages.
See also the Greek Rite diocese of Pittsburgh, and the Latin Rite diocese entries.
New Catholic Dictionary