Garage conversion rules in McHenry County, IL — sometimes called garage-to-ADU or accessory living unit conversions — govern permits, ceiling height, egress, and parking replacement.
In unincorporated McHenry County you cannot convert a detached garage or other accessory structure into living quarters unless it qualifies as a permitted ancillary dwelling unit under the UDO. Otherwise, an accessory structure may not be used as a dwelling.
UDO § 16.56.050A.1.a is explicit: no accessory structure may be used as a dwelling unit unless permitted as an ancillary dwelling unit under § 16.56.030O. That means converting a detached garage into a habitable unit is only allowed if it meets the ADU standards, including well/septic approval by the McHenry County Department of Health, the two-bedroom cap, owner occupancy, and the one-ADU-per-lot limit. Converting attached garage space into additional living area of the principal home is a building-permit matter subject to setbacks and building code. Incorporated cities such as Crystal Lake and Woodstock apply their own municipal codes.
An illegal conversion is a zoning violation enforced by the Zoning Enforcement Officer; unpermitted dwelling use must cease or be legalized as an ADU through the required approvals.
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See how McHenry County's garage conversions rules stack up against other locations.
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