The Mid-Suburban League (MSL) is an Illinois High School Association recognized high school extra-curricular league which includes twelve schools located in the northwest suburbs of Chicago, Illinois. The conference is split up into two divisions for all interscholastic activities. The primary criteria for the separate divisions is geography, with the schools in the West Division being located west of IL Route 53 and the schools of the East Division being east of it. However, the schools of the western division are also larger than the schools of the eastern division.