Better Education. Brighter Future.

Trinity Catholic High School History

Founded in the proud tradition of Mercy, St. Thomas Aquinas, Rosary, and St. Thomas Aquinas-Mercy

Trinity Catholic High School traces its educational roots back to Mercy High School that opened its doors as an Archdiocesan co-educational high school in 1948. The Sisters of Mercy served students in the central areas of St. Louis City and St. Louis County for close to 40 years before Mercy closed in the spring of 1985 and merged with St. Thomas Aquinas High School in Florissant.

St. Thomas Aquinas was named after the 13th century philosopher and patron saint of education and opened in 1954 in a building at Sacred Heart Parish in Florissant. Four years later, Aquinas, led by the Sisters of St. Joseph, moved to its permanent location on Dunn Rd. in Florissant.

The merger of Mercy and St. Thomas Aquinas High Schools formed St. Thomas Aquinas-Mercy High School in the fall of 1985 and the legacy of quality, Catholic education continued on the former Aquinas campus.  

In 1961, the Archdiocese of St. Louis opened Rosary High School in Spanish Lake in collaboration with the School Sisters of Notre Dame. For over 40 years Rosary High School educated young men and women with dedication to Mary, the mother Jesus Christ and Our Lady of the Rosary.


The decision was made in 2002 to merge St. Thomas Aquinas-Mercy and Rosary High School beginning with the 2003-’04 school year. It was determined that both schools would close and Trinity Catholic High School would open in the fall of 2003 on the former Rosary campus.

For over a decade Trinity Catholic High School has lived up to its rich history by providing the young men and women of North County and the surrounding areas a quality, college preparatory education featuring state-of-the-art technology, an outstanding core curriculum and a wide range of elective class offerings.