1833 - Arrival of First Irish Immigrants in Derby.

1845 - Donation of Land for Catholic Church by Anson G. Phelps (a non-Catholic)
1845 - First Catholic Church Built in the Valley

1847 - Founding of Old St. Mary's Cemetery
1851 - St. Mary Parish Established

1852 - Church Enlarged
1857 - Church Enlarged

1870 - Establishment of Ansonia Parish
1883 - Church Rebuilt
1885 - Arrival of Sisters of Mercy

1885 - Establishment of St. Mary's School in Basement of Church

1887 - Founding of Mount St. Peter's Cemetery

1897 - New Elementary School Built

1904 - Convent built
1932 - Parish Center Opened
1935 - Opening of Catholic Community House

1948 - Church Rededicated
1954 - New Elementary School Built during pastorate of Monsignor Quinn.

1968 - Cemetery Board took over management of
Catholic cemeteries of the Archdiocese of
Hartford

1969 - Convent and old St. Mary's School on Elizabeth St. were razed

1971 - Church Exterior Painted

1972 - Church Interior Painted

1972 - Three co-pastors named (an innovation in archdiocese of Hartford) as follows: Rev. Joseph R DeCarolis, Rev. James V. Hickey, Rev. Charles T. Kennedy

1974 - Church remodeled and redecorated. It was rededicated by Archbishop John F. Whealan