Kankakee County, IL Accessory Structures: ADU Rules (2026)

Kankakee County Code § 121-283, titled Lots, sets the ground rules for how many principal dwellings a parcel may carry. Subsection (b), Number of buildings on a lot, states that in the agriculture, residence, and rural estate districts, every nonagricultural single-family dwelling hereafter erected or structurally altered shall be located on a lot, and there shall be not more than one such dwelling on a lot. Read together with § 121-281's accessory-building rules, that means a homeowner in the A1, A2, R1, R2 or RE districts cannot convert a garage, barn or other accessory structure into a second, independently rentable dwelling unit, nor build a detached ADU, without first securing relief from the county.

The one-dwelling-per-lot rule targets nonagricultural residential conversions and does not prevent a homeowner from housing extended family inside the single permitted dwelling. Anyone who wants a second unit on an unincorporated lot needs to petition the Zoning Board of Appeals for a variation or a planned unit development under Article IV, since departures from the one-dwelling standard proceed only through that special-use process. Absent that relief, the Planning Department will not issue a building permit for a second principal dwelling, converted garage apartment, or other accessory dwelling unit on a lot already carrying one.