ZIP Code boundaries in Chicago. The data can be viewed on the Chicago Data Portal with a web browser. However, to view or use the files outside of a web browser, you will need to use compression software and special GIS software, such as ESRI ArcGIS (shapefile) or Google Earth (KML or KMZ).
data.cityofchicago.org (2013). Boundaries - ZIP Codes [Illinois--Chicago]. City of Chicago Data Portal. https://data.cityofchicago.org/d/gdcf-axmw (dataset)