DuPage County, IL Environmental Rules: Flood Zones (2026)

DuPage County's Countywide Stormwater and Floodplain Ordinance is codified at Chapter 15 of the DuPage County Code and is one of the strictest county-level floodplain regulations in Illinois. The ordinance was developed by the DuPage County Stormwater Management Planning Committee after the devastating August 1987 and July 1996 floods and applies to all 39 municipalities plus unincorporated areas.

Section 15-28 (Building Protection) requires that within the boundary of the regulatory floodplain, all usable space in new buildings, or added to existing buildings, must be elevated, floodproofed, or otherwise protected such that the lowest entry is at least two feet above the nearest base flood elevation (BFE). This two-foot freeboard exceeds the NFIP minimum of one foot. Floodproofing devices must operate without human intervention, and any electrical components must have a backup power source. Floodproofing must be certified by a licensed professional engineer.

The regulatory floodplain is defined using FEMA Flood Insurance Rate Maps (FIRMs) as adopted and modified by the County. Development in the SFHA requires a stormwater permit; some municipalities have amended the ordinance to require three feet of freeboard.