The first Mass to be celebrated in the district was said for a small group of Irish immigrants in 1818 by Fr. O'Reilly who travelled from Toronto to say Mass in various homes.  St. Peter Church was built in 1823 of log construction.  This was replaced by a frame building in 1850 and then replaced by the current brick building in 1882.  At some point it was closed and did not reopen until 1938.  

In 1822, well before the town of Milton was even incorporated, the nascent community around Jasper Martin's mill was home to only 5 Catholic families.  It is believed that the first Mass was celebrated in 1882 in the home of the O'Hara family.  Mass was celebrated once a month in various homes until the first Roman Catholic Church, St. Andrew, was built in 1859 on Pine Street.  The Parish was cared for by priests from Oakville and Burlington until 1938, when the Bishop appointed a resident Priest, Monsignor J.B.Ryan, to the parish.  The church is currently home to the administrative offices of the Milton Public Library.

​Around 1938, a used converted rail car was brought from Hamilton to Milton Heights.  It was converted to a chapel and named Blessed Margaret Mary Church and served the people living west of Milton.

​In 1942, a new church was completed in Milton Heights.  The church was dedicated to Our Lady of Victory in the Prayerful hope that, through her intercession, the war would end.  Both Our Lady of Victory Church and St. Peter Church were operated as mission churches of the Holy Rosary Parish in order to serve the needs of the rural communities in those areas.  Both churches were served by the priests from Holy Rosary until recent years. 

​The site for the present Holy Rosary Church was purchased in 1953 by Fr. J.P. Lardie and under his direction, the parish hall was built.  The Hall served as the new parish church until the present church was completed in 1966.  His Excellency, the Most Reverend J.F. Ryan, Bishop of the Diocese of Hamilton, officiated at the opening ceremonies and celebrated the first Mass on June 26, 1966.
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Our parish serves more than 7000 families in and around Milton.  We have 5 elementary schools: Holy Rosary, Our Lady of Victory, Queen of Heaven, St. Anthony of Padua. and St. Peter.  Holy Rosary Parish also serves our local Catholic high school, Bishop Reding.