Surprisingly, not much has been written about St. Mary Church in Newmarket other than what can be found on the first Spiritual Report to the Bishop of Manchester. Interestingly enough, the report does not give the name "St. Mary" to the Church but simply records it as "Parish of Newmarket, N.H."

The Church was given the name "St. Mary" some time later, but apparently not without a fight. The first recorded Baptism on May 30, 1878, lists the name of the church as St. Patrick. In 1888, the name was changed to St. Mary.

The Newmarket Church was organized as a separate parish in 1878 under the newly appointed pastor, Rev. John T. McDonnell. Prior to that, Father McDonnell served the Catholic population of Newmarket from Haverhill, MA. He is recorded as celebrating the first Mass in town in 1848. Every two weeks a priest would visit the area either from Exeter, Portsmouth, Dover and as far away as Keene.

In 1852, the Catholics in Newmarket were numeorus enough became a mission of St. Mary Church (later renamed Immacualte Conception) in Portsmouth. In 1859, it would become a mission of St. Bernard Church (later renamed St. Michael Church) in Exeter. By September 28, 1868, sufficient funds were raised by the growing Catholic population to purchase the Universalist Church in Newmarket. Fr. Thomas Walsh (of Exeter) supervised the conversion of this building into an edifice that the Catholic population took great pride in and would now call home. They would have to wait another ten years, however, before they received their own resident pastor and updated status to a parish church.

By 1878, the Catholic population of Newmarket had grown to "about 800." The number of Catholic clergy had also grown and there were now more priests available to serve the spiritual needs of the people. St. Mary Church would benefit from this increase in clergy as it would be assigned its first full time pastor. The Right Reverend James A. Healy, Bishop of Portland, Me, dedicated the Newmarket Church, now called St. Patrick in 1878. In attendance at the ceremony were Faher McDonnell, Father Murphy of Haverhill, Ma, and Father O'Callaghan of Portsmouth.

In 1878, the Sacrament of Confirmation was administered in St. Mary Church by Bishop Healy. During that same year, land was purchased for the Cemetery. The parish church would be "considerably" updated in 1882. On February 1, 1886, the first parish school was opened. Thirty pupils were enrolled in this "French" school taught by a "Frenchman." On January 16, 1889, the parochial residence was built and the end of the year saw the purchase of a tract of land for a new Catholic Church which was dedicated in October of that same year, now under the name of St. Mary. When the transition was made to the new Church, the old building became a school until it was sold in 1910. At that time a new school was opened and run by the Sisters of the Holy Cross. St. Mary School would close its doors for good in 1972 thus bringing eighty-six years of Catholic education in Newmarket to an end.

St. Mary Church has been a stabilizing influence in Newmarket and a place that many consider to be their spiritual home. There is not much that exists in the parish records concerning the Sacred Heart Mission in Newfields. In 1880, the Catholic population was a Mission of St. Michael church in Exeter. The present Church building was acquired by Bishop Healy on June 8, 1881 and it was dedicated on November 30, of the following year. On July 26, 1947, it became a mission of Newmarket and remained as such until it was closed in 2005.