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Illinois Compiled Statutes

405 ILCS 5/1-116 (2026)

Intellectual disability

✓ current as of May 2026
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(405 ILCS 5/1-116) (from Ch. 91 1/2, par. 1-116)
    Sec. 1-116. Intellectual disability. "Intellectual disability" means a disorder with onset during the developmental period (before the individual reaches age 22), that includes both intellectual and adaptive deficits in conceptual, social and practical domains. The following 3 criteria must be met: (1) deficits in intellectual functions such as reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning from experience confirmed by both clinical assessment and individualized, standardized intelligence testing (generally indicated with an IQ score of about 70 or below), (2) deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, the adaptive deficits limit functioning in one or more activities of daily life, such as communication, social participation, and independent living, across multiple environments, such as home, school, work, and community, and (3) onset of intellectual and adaptive deficits during the developmental period. This definition does not supersede the "intellectual disability" definition in Section 1.1 of the Firearm Owners Identification Card Act which is required to be applied under that Act for the purpose of mandatory reporting.
(Source: P.A. 102-972, eff. 1-1-23.)

    
Notes of Decisions
Cited in 14 cases (6 in the last 5 years), 1999–2026 · leading case: People v. Wilson, 2020 IL App (1st) 162430 (Ill. App. Ct. 2020).
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People v. Wilson, 2020 IL App (1st) 162430 (Ill. App. Ct. 2020). · cites it 2× “Prior to 2012, section 1-116 defined the term “mental retardation” as “significantly subaverage general intellectual functioning which exists concurrently with impairment in adaptive behavior and which originates before the age of 18 years.”
People v. Danial W. (In Re I.W.), 2018 IL App (4th) 170656 (Ill. App. Ct. 2018). · cites it 5× “¶ 17 The assistant state's attorney handed Osgood a copy of section 1-116 of the Mental Health and Developmental Disabilities Code (Code) ( 405 ILCS 5/1-116 (West 2016) ), which defined an "intellectual disability" as "significantly subaverage general intellectual functioning…”
In re I.W., 2018 IL App (4th) 170656 (Ill. App. Ct. 2019). · cites it 5× “¶ 17 The assistant state’s attorney handed Osgood a copy of section 1-116 of the Mental Health and Developmental Disabilities Code (Code) (405 ILCS 5/1-116 (West 2016)), which defined an “intellectual disability” as “significantly subaverage general intellectual functioning…”
In re O.B., 2022 IL App (4th) 220419 (Ill. App. Ct. 2022). · cites it 4× “nois Compiled Statutes, Chapter 750, Section 50/1(D)(p) [(750 ILCS 50/1(D)(p) (West 2020))] in that he is unable to discharge the parental responsibilities supported by competent evidence from a psychiatrist or clinical psychologist of mental impairment, mental illness, or…”
In re A.R., 2023 IL App (1st) 220700 (Ill. App. Ct. 2023). “She is unable to discharge parental responsibilities because of mental impairment, illness, or retardation as defined in 405 ILCS 5/1-116, and/or is developmentally disabled as defined in 405 ILCS 5/1-106, and there is sufficient justification to believe that such inability to…”
In re S.W.N., 2016 IL App (3d) 160080 (Ill. App. Ct. 2016). · cites it 2× “" 405 ILCS 5/1-116 (West 2010). Effective January 1, 2012, the term "mental retardation" was replaced by the term "intellectual disability," while the definition remained the same.”
In re K.B., 2019 IL App (4th) 190496 (Ill. App. Ct. 2020). “of unfitness are any one or more of the following ***: *** (p) Inability to discharge parental responsibilities supported by competent evidence from a psychiatrist, licensed clinical social worker, or clinical psychologist of mental impairment, mental illness[,] or an…”
In re S.W.N., 2016 IL App (3d) 160080 (Ill. App. Ct. 2016). · cites it 2× “” 405 ILCS 5/1-116 (West 2010). Effective January 1, 2012, the term “mental retardation” was replaced by the term “intellectual disability,” while the definition remained the same.”
In Re M.M., 709 N.E.2d 259 (Ill. App. Ct. 1999). “Section 1-116 of the Mental Health and Developmental Disabilities Code ( 405 ILCS 5/1-116 (West 1996)) defines mental retardation as follows: *Page 566 "`Mental retardation' means significantly subaverage general intellectual functioning which exists concurrently with impairment…”
In re K.D., 2026 IL App (4th) 251255-U (Ill. App. Ct. 2026). · cites it 3× “d of April 7, 2024, through January 7, 2025, pursuant to section (1)(D)(m)(ii) of the Adoption Act (750 ILCS 50/1(D)(m)(ii) (West 2024)) and (2) is unable to discharge parental responsibilities, supported by competent evidence from a clinical psychologist of an intellectual…”
In re G.W., 2022 IL App (5th) 220126-U (Ill. App. Ct. 2022). · cites it 2× “§ 1(D)(m)(ii)); and (4) she was unable to discharge parental responsibility, as supported by competent evidence from a clinical psychologist of mental impairment, mental illness, or intellectual disability as defined in section 1-116 of the Mental Health and Developmental…”
In the Interest of A.R., 2022 IL App (1st) 220700-U (Ill. App. Ct. 2022). “She is unable to discharge parental responsibilities because of mental impairment, illness, or retardation as defined in 405 ILCS 5/1-116, and/or is developmentally disabled as defined in 405 ILCS 5/1-106, and there is sufficient justification to believe that such inability to…”
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