In Illinois, government agencies are required to produce public documents when asked. The governing statute is the Freedom of Information Act. There is a federal law with the same name.
All of the documents and data we publish on this site were received through a series of FOIA requests. You can request information from the Chicago Police Department through foia@chicagopolice.org and from the Civilian Office of Police Accountability.
The process is supposed to be fairly simple - you submit a request to the correct agency, and they either produce the documents you requested or deny your request based on a list of exceptions delineated in the statute. In real life, it’s a lot slower.
Here are some resources to get you started:
MuckRock - a free site for making and seeing requests
A list of the FOIA contacts for all IL state agencies
A more complete list of all FOIA officers at the state, county, and municipal levels
A how-to guide from the Better Government Association