Parole allows prisoners who have served a significant percentage of their sentences to go before a parole board and demonstrate they have rehabilitated themselves and are no longer a threat to society. It gives inmates an incentive to educate themselves, gain skills and get mental health care behind bars. It gives prisons a reason to provide those services.
But Illinois stopped its across-the-board parole program in 1978. Inmates who were sentenced before then still periodically ask the Illinois Prisoner Review Board for parole, but there aren’t many of them left. Most inmates sentenced since then serve out a predetermined percentage of their sentences, and then they are freed on what is technically mandatory supervised release, even though people often refer to it as parole.