Mater Dei Catholic High School, 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.

Breese is a city in Clinton County, Illinois, United States. Breese is the most populous city completely within Clinton County. As of the 2020 census, the population was 4,641, the majority of whom are of German ancestry. Breese is part of the Metro-East region of the Greater St. Louis metropolitan area.