(1) The 1935 Club
The CSFL (also known as TCSFL) was founded in 1935 as chapter #14 of the SFL, the club attracted members including founder Walter Dennis, Paul McDermott, Jack Darrow, Allen Kline, Otto Binder, Earl Binder, Jack Binder, and William Dellenback. Sam Moskowitz called it "the outstanding chapter of the time."
Three of the members, Darrow, Binder, and Dellenback, planned to visit New York that summer to meet members of the New York chapter of the SFL. Charles D. Hornig planned a chapter meeting to take place at the offices of Wonder Stories, but the Chicago delegates arrived a day late and missed the meeting, instead visiting with Hornig, Mort Weissinger, and Julius Schwartz. Arguably, had this meeting happened, this would have been the first science fiction convention.
The club published the clubzine The Fourteen Leaflet from November 1935 through Spring 1937. In 1937, it severed its tiesl witht he SFL and renamed itself the Chicago Science Fiction Club, but by the time the final issue was published, many club members had left Chicago and the club soon went dormant.
(2) The 1962 Club
An entirely new club with the same name was formed around 1962 by Rosemary Hickey when the University of Chicago SF Club fell apart. The new version held monthly meetings on the first Saturday night of each month (except in months when a convention took place) at the home of Rosemary Hickey at 2020 North Mohawk Street and later at the home of George Price.
At Chicon III in 1962, they sponsored an exhibition of the art of Richard M. Powers on the Saturday of the convention. The league compiled the exhibit separately from the con and paid rent on the room themselves, asking con-attendees for voluntary donations to offset the cost.