In 1954, an increasing enrollment led the need for a new high school building, located just to the east of the convent.

On September 5, 1957, 470 girls began classes at the new Marymount High School facility, which today serves as the main building of the Trinity campus.

At the same time the Vincentian Sisters of Charity opened Lumen Cordium High School in Bedford, attracting nearby students who might otherwise have enrolled at Marymount.

Two years later the Byzantine Catholic High School in Parma closed, and a number of students transferred to Trinity.

[3] The students study a college-prep curriculum including Advanced Placement coursework in subjects such as English, Calculus, History, Spanish, Government and Art.