The history of St. Teresa High School goes back over a century to 1866, when the Sisters of the Holy Names of Jesus and Mary opened a school and named it the Academy of St. Teresa. In 1868, the Sisters of the Ursuline Order from New York took over the school, and in 1873 the present Order of Ursuline Sisters came from Alton, Illinois.

In 1874, the school was located on the 400 block of East Eldorado Street. In 1913, the school was moved to 2700 N. Water Street. At this time, it became an all girl’s boarding school. As the school became well-known, need for additional space became obvious. In 1930, the Ursuline Nuns requested that Bishop Griffin extend the girls academy. Bishop Griffin’s decision was to extend the girls academy, in return, the nuns were asked to build a co-ed building. As the enrollment enlarged, an addition of eight classrooms and gymnasium were dedicated by Bishop O’Connor in 1955.

When in 1930 St. Teresa Academy became a co-educational school under its new title, St. Teresa High School, Sister Loretto Boland was appointed its first principal. During her ten years as principal, Sister Loretto guided and shaped the policy of the school, gaining for its recognition as one of the outstanding co-educational schools of the state.

On August 29, 1996, the school was purchased from the ownership of the religious order of Ursuline Sisters. The St. Teresa High School Corporation purchased the school to continue the mission of providing quality Catholic Christian education to the Decatur area community.

St. Teresa has held continuous accreditation since 1932 from the North Central Association of Colleges and Secondary Schools and the Illinois State Department of Education. The school is also a member of the National Catholic Educational Association and the Illinois High School Association.