405 ILCS 5/1-116 : Health and Safety — Mental Health — Mental Health and Developmental Disabilities Code — Chapter I. Short Title and Definitions —116 - Intellectual disability TEXT PDF "Intellectual disability" means significantly subaverage general intellectual functioning which exists concurrently with impairment in adaptive behavior and which originates before the age of 18 years. 405 ILCS 5/1-116 P.A. 80-1414. Amended by P.A. 097-0227,§ 94, eff. 1/1/2012.