Accessory Structures in McHenry County, IL (2026)
4 rules for unincorporated McHenry County, Illinois.
Verified from official government sources
ADU Rules
Unincorporated McHenry County allows one ancillary dwelling unit per lot under UDO § 16.56.030O, attached to the house or built as a freestanding structure. The lot must stay owner-occupied, the unit is capped at two bedrooms and a 900-square-foot footprint, and mobile homes or RVs cannot serve as the unit. Detached units cap out at 35 feet and follow the same setbacks as the principal home.
Accessory Dwelling Units in Unincorporated McHenry County
Some RestrictionsMcHenry County UDO § 16.56.030O
O. Dwelling Unit, Ancillary. ... 5. Ancillary dwelling units shall be limited to no more than 2 bedrooms. 6. Ancillary dwelling units shall not exceed the size and scope of the principal residence. 7. Lots or parcels containing an ancillary dwelling unit shall be owner occupied. The owner may reside in either the principal residence or the ancillary dwelling unit. No one else shall occu...
Shed & Carport Rules
A carport is an accessory structure under the McHenry County UDO. In R-1, R-2 and R-3 residential districts detached accessory structures are limited to 14 feet (flat/mansard roof) or 18 feet (pitched roof) tall, and must sit at least 10 feet from any lot line.
Carport Rules in Unincorporated McHenry County
Some RestrictionsMcHenry County UDO § 16.56.050A.2.a(2)
In the R-1, R-2, and R-3 Districts, detached accessory structures are limited to fourteen (14) feet in height for a flat or mansard roof design, and eighteen (18) feet in height for a pitched roof design.
Garage Conversions
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.
Garage Conversion Rules in Unincorporated McHenry County
Some RestrictionsMcHenry County UDO § 16.56.050A.1.a
No accessory structure may be used as a dwelling unit, unless permitted as an ancillary dwelling unit in accordance with § 16.56.030O.
Tiny Homes
Unincorporated McHenry County allows a tiny house as a second unit on a lot only through the zoning code's Ancillary Dwelling Unit standard, not as a stand-alone tiny-house category. An ancillary unit is capped at two bedrooms, 900 square feet if detached, and one per lot, the lot must be owner-occupied, and mobile homes or RVs cannot serve as the unit.
McHenry County Tiny Home & Accessory Dwelling Rules
Some RestrictionsMcHenry County UDO § 16.56.030(O), Dwelling Unit, Ancillary
O. Dwelling Unit, Ancillary. ... 5. Ancillary dwelling units shall be limited to no more than 2 bedrooms. 6. Ancillary dwelling units shall not exceed the size and scope of the principal residence. 7. Lots or parcels containing an ancillary dwelling unit shall be owner occupied. The owner may reside in either the principal residence or the ancillary dwelling unit. No one else shall occupy the o...
All McHenry County ordinances
See every category we cover for McHenry County: parking, noise, fences, fires, animals, pools, and more.
McHenry County Ordinance Hub →