Mater Dei Catholic High School (often called Breese Mater Dei), is a Catholic, co-educational high school in Breese, Illinois, United States, in the Roman Catholic Diocese of Belleville. It was founded in 1954 through the merger of St. Dominic's High School in Breese and St. Mary's High School in Carlyle, Illinois. The academic program is accredited by North Central Association of Colleges and Schools, and holds a Certificate of Recognition from the Illinois State Board of Education.