The Ursuline Sisters founded St. Teresa High School as a coeducational high school in 1930. In 1996, the Ursuline Sisters withdrew their sponsorship of the school and a not-for-profit corporation was formed to assume ownership and control of St. Teresa High School. A nine member Board of Directors supervises and controls the business affairs of the corporation.

The Board of Directors of St. Teresa High School is responsible for ensuring that the school accomplishes its mission as an accredited Catholic secondary school serving the Decatur, Illinois area. The Board is composed of nine voting directors; one director is a member of the Decatur Deanery of Priests, while eight are lay directors. In addition to the nine voting directors, there are two ex-officio non-voting directors, namely, the Bishop of the Roman Catholic Diocese of Springfield and the school Principal.