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Illinois Compiled Statutes

405 ILCS 5/1-129 (2026)

Mental illness

✓ current as of May 2026
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(405 ILCS 5/1-129)
    Sec. 1-129. Mental illness. "Mental illness" means a mental, or emotional disorder that substantially impairs a person's thought, perception of reality, emotional process, judgment, behavior, or ability to cope with the ordinary demands of life, but does not include a developmental disability, dementia or Alzheimer's disease absent psychosis, a substance use disorder, or an abnormality manifested only by repeated criminal or otherwise antisocial conduct.
(Source: P.A. 100-759, eff. 1-1-19.)


 
    (405 ILCS 5/Ch. II heading)
CHAPTER II
RIGHTS OF RECIPIENTS OF MENTAL HEALTH
AND DEVELOPMENTAL DISABILITIES SERVICES


 
    (405 ILCS 5/Ch. II Art. I heading)
ARTICLE I. RIGHTS

    
Notes of Decisions
Cited in 7 cases (1 in the last 5 years), 2006–2022 · leading case: In re O.B., 2022 IL App (4th) 220419 (Ill. App. Ct. 2022).
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In re O.B., 2022 IL App (4th) 220419 (Ill. App. Ct. 2022). “(West 2020)) defines the terms “mental illness” (405 ILCS 5/1-129 (West 2020)), “intellectual disability” (405 ILCS 5/1-116 (West 2020)), and “developmental disability” (405 ILCS 5/1-106 (West 2020)).”
In re Commitment of Chester, 2017 IL App (1st) 160979 (Ill. App. Ct. 2017). “” 405 ILCS 5/1-129 (West 2006). Consistent with Dr.”
In re Commitment of Chester, 2017 IL App (1st) 160979 (Ill. App. Ct. 2017). “” 405 ILCS 5/1-129 (West 2006). Consistent with Dr.”
In re Diana M. (Ill. App. Ct. 2006). · cites it 2× “" 405 ILCS 5/1-129 (West 2004). The State is required to prove the basis for involuntary admission by clear and convincing evidence.”
In re Commitment of Chester, 2017 IL App (1st) 160979 (Ill. App. Ct. 2017). “” 405 ILCS 5/1-129 (West 2006). Consistent with Dr.”
In re T.M., 2020 IL App (3d) 180086-U (Ill. App. Ct. 2020). ““ ‘Mental illness’ means a mental, or emotional disorder that substantially impairs a person’s thought, perception of reality, emotional process, judgment, behavior, or ability to cope with the ordinary demands of life, but does not include *** a substance use disorder ***.”
In re Charles K. (Ill. App. Ct. 2010). “In accordance with the definitions of "mental illness" and "person subject to involuntary admission" set forth in sections 1-129 and 1-119 of the Code (405 ILCS 5/1-129, 1-119 (West 2008)), respectively, the jury was instructed as follows: "Mental illness means a mental or…”
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