St Joseph’s Parish, Iona, was established by the late Archbishop Carr, Archbishop of Melbourne, in 1905.  It then covered the area from Nar Nar Goon North to Tonimbuk in the North and Koo Wee Rup to Lang Lang in the south.  The Penal Settlement on French Island was also included.  This Penal Settlement was later transferred to the Dalyston (now Cowes) parish.  Prior to that this whole area belonged to St John’s Parish, Dandenong.  The first Parish Priest was Fr J Byrne.  Then there were churches in Iona, Nar Nar Goon and Koo Wee Rup.  The first Assistant Priest, Fr Goldsprink, was appointed in 1909.  In 1946 the Koo Wee Rup – Lang area was cut off from the Iona Parish to become St John the Baptist Parish, Koo Wee Rup.

In 1950 Holy Family Parish, St Mary’s, (renamed Maryknoll in 1955) was established as a separate parish under the pastoral leadership of Fr Wilfred Pooley in part of the Tynong North area.  In 1968 it was amalgamated with St Joseph’s Parish, Iona, and the new parish became known as St Joseph’s Parish, Iona-Maryknoll.  Fr Wilfred Pooley became the first Parish Priest of this newly formed parish.  In October 1959 the Iona and Maryknoll parishes together with the Berwick, Pakenham, Koo Wee Rup, Korumburra, Dalyston (now Cowes) and Wonthaggi parishes, became part of the Diocese of Sale.

Another major change came in 2000.  Then the Iona-Maryknoll and Koo Wee Rup parishes were asked to go into Parishes in Partnership.  Fr Bernard Buckley was then appointed Parish Priest for both parishes.