The league continued to add schools as time moved forward with Argo joining in 1938 and Lockport in 1939.

The south suburbs continued to grow in popularity with school districts becoming larger and populations increasing.

In 1960, Joliet joined from the Big 8 and newly opened Thornridge High School was added to the league as well.

[1][2] Another mass exodus would occur in 1966 as Argo, Kankakee, Lockport and all three Joliet schools left in order to join the newly chartered Illini 8 Conference.

The last team to join this original version of the South Suburban was Thornwood in 1972, the same year the school opened.

[4] The conference covered a large geographic area and sociological spectrum "from the Indiana border to Joliet, from impoverished Ford Heights to affluent Frankfort, from virtually all-black Hillcrest to almost all-white Lincoln-Way Central and from Joliet, enrollment 4,993, to 1,066- student Rich South"[4] In 2004, the athletic directors voted 30–3, the principals' board of control voted 6–2, and the district superintendents voted 16–3 to approve a new conference realignment which was to take effect in 2006.

In April 2006, a federal civil rights lawsuit was filed against the schools which had left claiming that "(an) apartheid-like realignment used public funds to regress to separate but equal".