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

The county's Chapter 15.04 amendments to the 2021 International Building Code, adopted at § 15.04.010, rewrite IBC § 1612 to route flood-hazard construction through the McHenry County Stormwater Management Ordinance rather than the model code's own flood maps. Section 1612.3 states that the establishment of flood hazard areas "shall comply with the McHenry County Stormwater Management Ordinance," and where design flood elevations or floodways aren't already spelled out there, §§ 1612.3.1 and 1612.3.2 require the applicant to meet whatever the Stormwater Management Ordinance specifies for that riverine area. Section 1612.4 sets the actual construction standard: buildings and structures in a flood hazard area must be designed and built in accordance with the Stormwater Management Ordinance and with Chapter 5 of ASCE 7 and all of ASCE 24, the national flood-resistant design standards. Section 1612.5 then requires flood hazard documentation to be prepared to match both the Stormwater Management Ordinance and this building code.

The same flood-hazard trigger reaches into grading: § 1804.5, amending IBC Chapter 18, requires that grading or fill within an area established as a flood hazard area under § 1612.3 be qualified and approved in accordance with the McHenry County Stormwater Management Ordinance before work proceeds. Building permit review for this work sits with the Planning and Development Department, and where the local amendments conflict with the base IBC text, § 15.04.030 directs the more restrictive provision to control.