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

The Lake County Watershed Development Ordinance (WDO) is one of the strictest county-level stormwater ordinances in Illinois, enforced by the Lake County Stormwater Management Commission (SMC) under the authority of 55 ILCS 5/5-1062. The WDO applies countywide (including incorporated municipalities that have not achieved certified-community status). A Watershed Development Permit (WDP) is required for any of the following: site disturbance of 5,000+ sq ft, creation/modification of 15,000+ sq ft of impervious area, any work in a regulated floodplain/floodway, any impact to wetlands or isolated waters of Lake County (IWLC), or development near lakes/streams. Requirements include soil erosion and sediment control (SESC) plans, stormwater detention meeting release-rate criteria (0.04 cfs/acre for 2-yr, 0.15 cfs/acre for 100-yr), native vegetation buffers along watercourses, and floodway prohibitions on new habitable structures. Fox River, Des Plaines River, and Chain O'Lakes communities (including portions of Waukegan along the Waukegan River and Highland Park ravines) are heavily regulated. Municipalities like Libertyville, Lake Forest, Highland Park, Gurnee, and Waukegan also enforce their own stormwater codes consistent with or stricter than the WDO. Illicit discharges are governed by the Clean Water Act MS4 permit program and Illinois EPA (IEPA) under 415 ILCS 5.