Word Of God: The novel, which is based on the original screenplay (which bares only a slight resemblence to the final version), expands on some points, such as what Elwood was doing between Jake getting locked up and the beginning of the film (he worked in a aerosol can factory as a maintenence guy, which is how he got that glue can. In a deleted scene, in fact, he is shown working at the factory on the assembly line, before going to his boss's office to tell him that he's quitting to become a preacher).
The mall chase scene took place at Dixie Square Mall, a shopping mall in the Chicago suburb of Harvey that had already gone out of business in 1979 due to excessively high crime. The filmmakers set up fake storefronts within half of the mall (for instance, the Toys "R" Us seen in the film was actually a Walgreens). After filming finished, the building was left abandoned for thirty years before finally being demolished in 2012.
