The laying of the cornerstone for this "cathedral in the wilderness" attracted more than 4,000 people, and special trains were run from Boston and Norwood.

The history of Catholicism in Dedham begins in 1758, only 120 years after the settlement of the Contentment Plantation and fully two decades before the American Revolution.

[2][3][1] Eleven of them resettled in Dedham, and though the town and the Massachusetts Bay colony were both officially Congregationalist, they were allowed to reside here as French neutrals[4] until they returned to Canada in 1760.

[5] The few Catholics who lived in Dedham would have to travel 16 miles to St. Joseph's in Roxbury, the Cathedral of the Holy Cross on Franklin Street in Boston, or to St. Mary's in Waltham to attend Mass.

[11] For the next three years Slattery's 17-year-old brother-in-law would bring Father James Strain from Waltham and back each Sunday to minister to the needs of the small congregation.

[1][2][4][9][nb 2] By 1846, the Catholic community in Dedham was well established enough that the town became part of the mission of St. Joseph's Church in Roxbury.

[1][2][4][7] The flood of Irish immigrants escaping the Great Famine necessitated holding Mass in the Temperance Hall, often by Father Patrick O'Beirne.

[20] In February 1880, it was announced that a Protestant who had business in Boston had paid off the parish's $700 debt, allowing the congregation to commence work on a new building.

[24] The footprint of the Gothic church, which Father Johnson said was to be a "cathedral in the wilderness,"[25][26] measures 150' long by 65' wide, and the bell tower is 164' tall.

[10] After 20 years of working, praying, and fundraising from the meager immigrant wages of many of the parishioners, the Upper Church was finally completed.

It took so long that another architect had to take over but was, Father Fleming said, “almost too beautiful for ordinary use.”[2][8] The upper church was completed and dedicated by Archbishop Williams on September 9, 1900.

[1][26][33] In addition to Williams, Archbishop Sebastiano Martinelli, the papal delegate to the United States, attended, as did Bishop Denis Mary Bradley of New Hampshire.

[8] In the 1920s, with the building work completed, new pastor Father Henry A. Walsh was able to focus on the various groups and societies within the parish.

[35] Within months of arriving as pastor in 1929, Father George P. O'Connor began a parish school with three Sisters of St.

[42] One of the largest ministries in St. Mary's today in its Life Teen program, which ministers to high school aged youth.

[43] In 1880, the Town of Dedham set aside a portion of Brookdale Cemetery, just a block away from St. Mary's, for Catholics to be buried.

[45][46] Will Sexton and Mike Zimmerman were both teens in the program, and were ordained alongside Stoughton, MA LifeTeen alumnus Kevin Leaver in 2017, who was a Dedham CORE member before ordination.