In 1920, there were about 100 Catholics living in the vicinity of Chelmsford Center. The closest Catholic Church was St. John's located in North Chelmsford. Fr. Charles P. Heany, Pastor of St. John's, sponsored the movement and fund drive that allowed the Mission Church of St. Mary's to be built in 1926. The modest stucco structure was built on the estate of Lottie L. Adams on North Road at Fletcher Street (the present location).

For the next 5 years, St. Mary's retained its mission status under the direction of St. John's Pastors. In November, 1931 Cardinal William O'Connell decreed that St. Mary's become a separate Parish with Rev. Daniel F. Gorman as Pastor. Only then could records be kept at St. Mary's. Fr. Gorman served until his death in January, 1935.

In 1961, ground was broken for the present Church. The new St. Mary's Church was dedicated on October 5, 1962 and the first Mass was celebrated in the Church on October 7,1962 - Feast of the Most Holy Rosary.

During the past years, St. Mary's has grown from a Parish of 500 members to one of over 14,000 members. St. Mary's is a vibrant Parish where the spiritual and community needs of its members are addressed and met. The Parish Community, under the direction of Reverend Leo E. Martel, fosters an environment for the support and growth of the individual's relationship with God.