St. Mary's High School was originally envisioned by Father Robert Byrne in the 1880s, and was founded in 1885 as Loretto Academy by the Sisters of Loretto, with an initial enrollment of nine female students. Classes were held in local residences, moving numerous times to larger houses as enrollment grew. In 1889, the Sisters built a school on Sierra Madre, between Kiowa and Bijou, with the fourth floor serving as their residence. In 1897, St. Mary's Catholic Parish built a new church next door to Loretto Academy. In 1902, Loretto Academy was renamed St. Mary's School. At this time enrollment had grown to 250 boys and girls in classes from first grade through high school. 1904 saw the first graduation class of St. Mary's School, with two graduates. St. Mary's Parish purchased the school in 1912. In 1950, a new school was built on the southeast corner of Sierra Madre and Kiowa for first through eighth grade students, and the original building became the high school. A gym was built on the southeast corner of Sierra Madre and Bijou. Near the end of the 1950s, the school phased out the elementary grades to accommodate the larger number of students in the high school. In the early 1960s, the student population outgrew the current facilities, resulting in the building of the Catholic Education Center, which opened prior to Fall 1964. Throughout this period the Sisters of Loretto continued to provide the teaching staff of the school, mainly nuns of that order but also including lay professionals. Graduating classes of this time period routinely included more than 100 students. In the mid-1970s, due to the national shortage of sisters, the teaching staff became predominantly professional educators. On February 11, 1987, with some controversy the diocese announced the closure of St. Mary's High School due to mounting debt. A group of parents formed the Committee for Catholic Secondary Education and reopened the school in Fall 1987 as a Catholic high school not affiliated with the diocese, though still renting the original school facilities. In 1991 the diocese informed the school they would be selling the school buildings, and a search for a new site was undertaken. The school moved to its current location at 2501 East Yampa Street on August 23, 1992. The site had sufficient room for significant expansion, and the campus was improved with the additions of a chapel, additional classrooms, the Cove, stage, gymnasium, art and photography labs, and fitness center. In 2006 the school opened a multimillion-dollar sports facility on in the Cragmor neighborhood near the main campus, named The Grace Center for Athletics and Community Service.
