The league had somewhat fluid membership over several decades. As the population of suburban Chicago grew (and the number of high schools with it) schools began leaving to join newer conferences such as the West Suburban Conference (started 1922), the Northwest Suburban (started in 1925, which later became the North Suburban Conference and Mid-Suburban League), and the South Suburban League (started in 1950). With more schools leaving (and newer suburban schools joining more geographically logical conferences), the Central Suburban League was founded in 1965, the last major conference to be carved from the old Suburban League. The last remaining bastion of the Suburban League started joining these other leagues, and finally folded after the 1974–1975 school year. As of the end of the 2007–08 school year, the past and present schools of the CSL have won 233 state titles in various IHSA sports and activities. They have finished in second place 261 times. Nearly half of these (105 state titles and 113 state runners-up) have been won by New Trier (or the two schools it was split into for a time, New Trier East and New Trier West). Evanston adds 47 state titles and 49 runner-up prizes. The league has remained stable (except for divisional realignment) since Niles North returned to the league in 1991. During Winter 2016, the CSL Athletic Directors voted 7-5 for a division realignment system. The system incorporates enrollment and athletic success in determining division placement. Every three years, points are tallied and the top six teams are placed in the South Division, while the other six are in the North Division. Before 2016, divisions were determined only by enrollment. Glenbrook North and Niles North wer the first schools to swap divisions in the 2019-2020 season. Timeline 1965 – CSL is formed by Deerfield, Glenbrook North, Glenbrook South, Maine South, Niles North, and Niles West. 1967 – Maine West joins the league, as does the newly opened New Trier West. 1971 – Maine North joins. 1972 – Highland Park and Niles East both join from the Suburban League. Maine East joins from the West Suburban Conference. This is the first year there are two divisions in the conference. 1974 – Maine North moves out of conference. 1975 – With the Suburban League now folded, Evanston, New Trier East, Waukegan East, and Waukegan West join. 1979 – Niles North leaves the league. 1980 – Niles East closes.