405 ILCS 15/1

In the event that any person is sentenced and committed under the laws of this State or the ordinances or resolutions of any municipal corporation or political subdivision to any penal or correctional institution other than the penitentiary or reformatory, any person 18 years of age or over may file with the Circuit Court a petition asserting that the person named in the petition has become subject to involuntary admission under the Mental Health and Developmental Disabilities Code since his commitment. The petition shall be accompanied by the certificate of a qualified examiner, psychiatrist, clinical psychologist or physician stating in reasonable detail the basis for the conclusion of said certificate that the person whose hospitalization is desired is subject to involuntary admission as that term is defined in Section 1-119 of the Mental Health and Developmental Disabilities Code.

The petitioner shall provide the State's Attorney and the person named in the petition with a copy of the petition.