Crystal Lake South High School, often referred to as "South" or "CLS," is one of three high schools in Crystal Lake, Illinois, and currently has a body of roughly 1916 students. As Crystal Lake's second oldest school, it was constructed from 1976 to 1978 and opened in September 1978 after Crystal Lake Community High School, now Crystal Lake Central High School, split into two schools due to the pressures of the population growth in the communities it served, Crystal Lake, a part of Lake in the Hills and a small portion of Algonquin. South graduated its first class in 1979 - this class consisted of approximately 250 seniors who were transferred from Crystal Lake Central High School. South graduated its first class who attended all four years in 1982.