605 ILCS 5/5-911

Impact fees shall be assessed by units of local government at the time of final plat approval or when the building permit is issued when no plat approval is necessary. No impact fee shall be assessed by a unit of local government for roads, streets or highways within the service area or areas of the unit of local government if and to the extent that another unit of local government has imposed an impact fee for the same roads, streets or highways.