Thanks to the production notes on the DVD version of TBC I now have the definitive desciption of the filming location used in TBC.
As I was able to piece together from various sources, the movie was filmed almost entirely at Glenbrook North High School, which is now an Illinois State Police Station!.
The library were the majority of the film is set was actually a HUGE set constructed from scratch in the Glenbrook North High School Gymnasium!. This amazing task was the work of the production designer. The detail that went into making this complete library is nothing short of amazing!. Next time you watch the movie take time out to appreciate how much work went into not only designing but constructing a complete life size school library! This had me fooled for the last 15 years, I thought it was a real library!
The library was designed to add the feeling of confinement relevant to the story.
The cast and crew were made to eat their meals in the school caferteria
During breaks in filming the cast and crew would play basketball in the smaller gymnasium.
The movie was shot almost entirely in sequence, which is another amazing aspect of this film
The football oval used at the end of the movie is located behind Glenbrook North High School, from which John Hughes graduated.
Part's of the movie "Ferris Bueller's Day Off" were filmed there aswell.
There is no suburb called Shermer, nor is there a Shermer High School. The name Shermer comes from Shermer Rd which is the street that Glenbrook North High School is located on. Although Glenbrook used to be known as Shermerville many decades ago.Here is a map showing the location