Some government agencies comply with public record laws by posting certain items on their website, so they don't have to charge fees or pay anybody to help the researcher.
The Illinois Department of Corrections makes all this information available to the public through links at https://idoc.illinois.gov/reportsandstatistics/prison-population-data-sets.html, https://idoc.illinois.gov/reportsandstatistics/prison-admission-data-sets.html, https://idoc.illinois.gov/reportsandstatistics/prison-exit-data-sets.html and https://idoc.illinois.gov/reportsandstatistics/parole-population-data-sets.html. We make it easy to find somebody on your family tree when you didnt know the person went to Illinois.
This is not a mugshot website. You can look up more information about somebody who is still in prison, at https://idoc.illinois.gov/offender/inmatesearch.html. You can continue tracing your family tree by contacting the Illinois department of Corrections for additional information about a former inmate who has been released.