10 ILCS 5/3-5
No person who has been legally convicted, in this or another state or in any federal court, of any crime, and is serving a sentence of confinement in any penal institution, or who has been convicted under any Section of this Code and is serving a sentence of confinement in any penal institution, shall vote, offer to vote, attempt to vote or be permitted to vote at any election until his release from confinement.
Confinement for purposes of this Section shall include any person convicted and imprisoned but granted a furlough as provided by Section 3-11-1 of the Unified Code of Corrections, or admitted to a work release program as provided by Section 3-13-2 of the Unified Code of Corrections. Confinement shall not include any person convicted and imprisoned but released on parole.
Confinement or detention in a jail pending acquittal or conviction of a crime is not a disqualification for voting.
10 ILCS 5/3-5