The birth of Most Holy Trinity Parish was announced in a letter from the Archdiocese to the Reverend Michael A. Condon, pastor of the Church of the Holy Family.  Dated, May 21, 1943, the letter asked Father Condon to "announce to the members of your congregation on Sunday, May 23rd, that after that day, all Catholics residing within the territory...will be under the jurisdiction of the Parish of Most Holy Trinity."

Catholic Education was an integral part of Most Holy Trinity Parish from its inception.  In September of 1945, several sisters of St. Benedict from St. Joseph, MN, moved into the convent at 4029 Utica Ave.  Kindergarten through sixth grade classes opened with four sisters and two lay teachers instructing 178 pupils.  Increased enrollment and space constraints necessitated discontinuance of the Kindergarten and the Sunday nursery.  The Sisters' recreation room in the basement of the convent was converted into a temporary classroom.  A seventh and eighth grade were added, and the first eighth grade graduation took place in 1948.

By 1951, the semi-basement building had become inadequate and a drive to enlarge the building was inaugurated.  By now, 262 students were enrolled in the school and they played an active part in expanding the parish by having their own fund drive.  In 1952, permission was given to complete the superstructure of the combination church and school.  The project added 6000 sq. ft. of floor space for 8 new classrooms and a church addition of 3500 sq. ft.  The first Mass in the completed building was held on Christmas Eve in 1953.