405 ILCS 5/1-106
"Developmental disability" means a severe, chronic disability, other than mental illness, found to be closely related to an intellectual disability because this condition results in impairment of general intellectual functioning or adaptive behavior similar to that of persons with ID, and requires services similar to those required for a person with an intellectual disability. In addition, a developmental disability: (1) is manifested before the individual reaches 22 years of age; (2) is likely to continue indefinitely; (3) results in substantial functional limitations in three or more of the following areas of major life activity: self-care, receptive and expressive language, learning, mobility, self-direction, capacity for independent living, or economic self-sufficiency; and (4) reflects the individual's need for a combination and sequence of special interdisciplinary or generic services, individualized supports, or other forms of assistance that are of lifelong or extended duration and are individually planned and coordinated . This definition does not supersede the "developmental 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.
405 ILCS 5/1-106