765 ILCS 330/4

Neither possibilities of reverter nor rights of entry or re-entry for breach of condition subsequent, whether heretofore or hereafter created, where the condition has not been broken, shall be valid for a longer period than 40 years from the date of the creation of the condition or possibility of reverter. If such a possibility of reverter or right of entry or re-entry is created to endure for a longer period than 40 years, it shall be valid for 40 years.