Fr. Therry, who arrived in May 1820, is known to have had a Mass station at the house of Major George Druitt. The house of a Mr. Hayes in South Creek was also used as a Mass station.

The first Catholic Church at St Marys was completed in 1875 and officially blessed by His Lordship Bishop Reynolds of Adelaide. Shortly after this Fr. James Phelan came to the area and was the Parish Priest at Penrith and from there he served the district of St. Marys. After retiring, he lived in a little cottage on Mamre Road in St Marys,  and on his death in 1898, he was buried in St. Marys Cemetery.

In 1880 the Sisters of St. Joseph arrived and their first two communities were at Penrith and St. Marys. The first church in St Marys was also used as a school and hall. It was known as St. Joseph’s Convent School , South Creek, St. Marys W.L. (Western Line). The school was established by Saint Mary of the Cross MacKillop.

The second Church was erected and opened in 1892,

The St. Thomas conference of the St. Vincent de Paul society was founded at St Marys on Sunday April 18, 1943. When Penrith Parish was created, St. Marys and surrounding districts were included in its boundaries. Late in 1946, however, St. Marys was set up as a parish in its own right, and included the districts of Mount Druitt, Rooty Hill, Horsley Park, Astral, Llandillo, Berkshire Park and Erskine Park. The first parish priest was Fr Michael Nelan. Fr. Thomas Kerr followed Fr. Nelan and he in turn was followed by Fr. James Page, who remained as parish priest for 28 years.

The present church was built during Father Page’s time. It was blessed and opened on May 13 1962.

The Salesians of Don Bosco took responsibility for the parish in 1998, with the first Salesian parish priest being Fr Peter Kerin SDB. The Don Bosco Youth Centre was built on nearby land and is staffed by priests, brothers and sisters. It is a popular venue after school, on weekends and during school holidays.