City of Chicago Homepage - www.cityofchicago.org

• City Departments
• Data Portal (part of the City's Transparency Initiatives)
• Citizen's Police Data Project (see also data on Public Safety at the Data Portal)

Encyclopedia of Chicago
The Encyclopedia of Chicago contains thousands of historical resources related to Chicago's history.

Google Books
Many publications from the City of Chicago have been digitized and those in the public domain (pre-1923) can be viewed in their entirety.  The screenshot below highlights the option to filter search results by date.

Chicago History Resources: Chicago Public Library
Explore Chicago's past with these resources from the Chicago Public Library. Its Municipal Reference Collection is a comprehensive group of documents from the City of Chicago, the Chicago Housing Authority, and the other local taxing bodies in the City.

IRAD: Illinois Regional Archives Depositories
Illinois Regional Archives Depositories (IRAD), a system administered by the State Archives to manage the archival records of local governments. IRAD at Northeastern Illinois University houses selected governmental records for Chicago and Cook County from the late 1800s to the early 1900s.