Triad High School is a high school located in Troy, Illinois. Triad serves the communities of Troy, St. Jacob, and Marine, Illinois, and small portions of Collinsville, Maryville, Glen Carbon, and Highland. The school district has a total area of 121.5 square miles (315 km2). The majority of Triad High School students live in Troy, Illinois, a town 18 miles (29 km) northeast of St. Louis, Missouri.