Some detainees were allegedly restrained for prolonged times, causing physical injuries and psychological trauma. In hundreds of cases, jail staff used a stun gun, Taser or pepper spray in the process, leading to death in some cases.
Human rights groups have long decried the use of restraint chairs in American jails and prisons, where they say the device is prone to misuse and abuse that is akin to torture.
The United Nations Committee Against Torture has urged U.S. officials to abolish the chairs, and Amnesty International has said inadequate training and supervision of their use has caused pain, injury and even death.
The same brand of chair used in many Illinois jails was also used at Guantánamo Bay.
However, records obtained by the Illinois Answers Project show the chairs continue to be used daily in some county jails.
You can read more on the Illinois Answer Projects investigation on restraint chairs at illinoisanswers.org.