Will County, IL Environmental Rules: Stormwater Management (2026)

The Will County Stormwater Management Ordinance (WCSMO), administered by the Will County Stormwater Management Planning Committee under 70 ILCS 1815 (Will County Stormwater Management Commission Act), is one of the most comprehensive stormwater regulations in Illinois. It applies countywide, including within most municipalities via intergovernmental agreement (certified communities include Joliet, Bolingbrook, Plainfield, Romeoville, Lockport, Frankfort, Mokena, and New Lenox). Key triggers: any development disturbing 0.5 acres or more, or creating 5,000+ sq ft of new impervious surface, requires a stormwater permit. Major developments require detention/retention sized for 100-year 24-hour storms, water-quality treatment for the first 1.25 inches of runoff, and compensatory storage at 1.5:1 for any fill within the 100-year floodplain. FEMA flood maps (Flood Insurance Rate Maps) govern floodplain boundaries, which are significant along the Des Plaines River (Joliet/Lockport/Romeoville), DuPage River (Plainfield/Naperville), Hickory Creek (New Lenox/Mokena/Frankfort), and Kankakee River (southern county). MS4 permits under the federal NPDES program and Illinois EPA regulate city-wide discharges. Illicit discharge enforcement is shared between Will County Land Use, municipalities, and the Illinois EPA.