Dayton’s early Catholic history isn’t very well-documented, either because the Catholics moved to other towns that had priests, or because the records are lost.
We know that Fr. Edward Fenwick said Mass in Dayton sometime in the spring of 1818. He was always crisscrossing the state on missionary journeys, even before he became Cincinnati’s first bishop in 1822; so presumably he stopped by Dayton several more times.
We know that Bishop Fenwick and Ven. Frederic Baraga (then a priest, soon to become a bishop) visited Dayton in 1831. Baraga said in a letter to the Leopoldine Association that he found “some lazy Catholics” there. He celebrated Mass in a private Catholic home, and later gave a talk at a Protestant church.
The first documented-by-name Catholics in Dayton were Robert Conway and his family. In 1832, they moved into Ice Alley, between First and Second St. (Now E. 1st and E. 2nd. And Google thinks it’s “Ice Avenue,” for whatever reason.) More known Irish and German Catholics moved to town in 1833. In December 1833, Father Louis Navarron (up north at Minster) wrote a letter asking a Father E.T. Collins (visiting in Dayton from Cincinnati) for a loan of some sacred vessels. So obviously the Dayton Catholics were getting some Masses from visiting itinerant missionary priests, as with most of Ohio. Other known visiting priests include Father Emmanuel Thienpont, Father Henry Damian Juncker (later the first bishop of Alton, IL), and Father Stephen Theodore Badin (the first Catholic priest ordained in the US).
The first known place used for Catholic worship in Dayton was the Conway place in Ice Alley. Later, as the number of Catholics grew, they switched to a one story brick meeting hall and bakery about a block away, on St. Clair St., across the street from what is now Cooper Park. (The brick building is now a parking lot.) Mass was in Latin, but sermons were in German, because German speakers outnumbered the Irish- and English-speaking Catholics.
In 1835, Mrs. Prudence Pierson donated a lot on Franklin Street, between Ludlow and Prairie, to the Archbishop of Cincinnati. Fr. Thienpont was told to begin raising money to build a church. 1300 dollars was collected that year from Protestants alone! In 1836, Fr. Thienpont was made pastor of Dayton’s parish-to-be, and continued collecting money. In 1837, construction began. The new church was consecrated by Archbishop Purcell on November 26, 1837. Dayton’s mother church was named “Emmanuel.”
By 1846, Dayton’s Catholic population had grown so much that a second parish was needed for the mostly Irish population on the east side of town. St. Mary’s (further east and south) was founded in 1859, and Holy Trinity (between St. Mary’s and St. Joe’s) was founded in 1861. These both served the German community. Other early parishes across the river from Emmanuel were St. John’s over in Edgemont, St. James, Resurrection (all three now consolidated as St. Benedict the Moor), Holy Name (Hungarian parish on Dale; now defunct), Corpus Christi (now joined up with Queen of Martyrs and Our Lady of Mercy), St. Agnes (my godparents’ and an uncle and aunt’s home parish, closed in 2006), and from 1916-1918, St. Gabriel’s Greek Catholic Church (on S. Summit St. (now S. Paul Lawrence Dunbar) near W. Fifth). Holy Angels (out by UD) and Sacred Heart (downtown) were in the middle of the older parishes. Further north from St. Joe’s were Holy Rosary, St. Adalbert (Polish), and Holy Cross (Lithuanian) (all now amalgamated with the Hungarian parish, St. Stephen). Further east of St. Joe’s were Holy Family, and St. Anthony (of Padua).
In the middle of a cholera epidemic, the Marianists came to Dayton in 1849 to help out at Emmanuel; and bought a property from Mr. John Stuart, in March 1850, which would eventually become the University of Dayton.
UPDATE: Info from Lamott’s History of the Archdiocese of Cincinnati (1821-1921); Drury’s History of the City of Dayton and Montgomery County, Ohio; and Fortin’s expanded history of the Archdiocese, Faith and Action. Also, the complete but sometimes nasty YWCA report on post-WWI immigrant neighborhoods, Foreigners in Dayton: An Investigation, which told me where St. Gabriel’s was.
Re: St. Gabriel’s, the author seems to think it was a Romanian Greek Catholic church, so if it had stuck around, it’d probably be under the Eparchy of Canton. Apparently the saga was like this: The Romanian community had been attending Holy Name and St. Stephen, with the Hungarians. They bought the defunct Summit Street United Brethren Church and started a new parish with Father Popo-Lupu. Father stayed for two years full time, then went to Canton, Ohio, coming back only once a month for Masses. (Possibly the parish became officially Greek Catholic at this time, connected to the Romanian-based eparchy back then.) At some point, obviously the whole thing died out. And why I have to go to a weird old YWCA report to find this out, when there’s three archdiocesan history books, I don’t know.