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

Significant Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Macon County, IL, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Default rule: Guest houses/apartments barred as accessory buildings
Path to allow: Special use permit, Board of Appeals hearing
Permit review agencies: County Regional Planning Commission, Health Dept.
Permit expiration: Void if work not underway within 1 year
Penalty: Up to $500 per offense, § 155.999

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Illinois under recent ADU streamlining laws. The Macon County, IL rules below cover local size, height, and setback requirements.

Summary

Macon County's zoning code does not allow guest houses, servants' quarters, apartments, or similar living units as accessory buildings on residential or agricultural lots. Section 155.051(B)(11) requires a special use permit from the Board of Appeals before any accessory structure can include separate living quarters.

These county ordinances apply to unincorporated areas of Macon County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

(11) Accessory building shall only be built for and used for permitted accessory uses. Guest houses, servants quarters, apartments, and the like shall not be permitted as accessory buildings, except when issued a special use permit.

View official code

Full Breakdown

051(B)(11), an accessory building on a zoning lot in the unincorporated county can only be built for a use that is itself a permitted accessory use, and the section specifically lists guest houses, servants' quarters, and apartments as uses that are not permitted as accessory buildings by right. A property owner who wants a detached structure with its own living space, the kind of arrangement often called an accessory dwelling unit or in-law suite elsewhere, cannot simply build it alongside the house the way a shed or garage is allowed.

181 goes to the Board of Appeals for a public hearing after the Administrative Officer refers the petition, with the County Regional Planning Commission and County Health Department submitting written recommendations before the Board decides. 047(C) and (D). 048(C)(1), reinforcing that the county treats any second living unit on a residential or agricultural lot as a use requiring case-by-case Board review rather than an as-of-right addition.

Violations & Fines

Building or occupying an unpermitted guest house or apartment as an accessory unit violates § 155.051 and is subject to the chapter's general penalty at § 155.999: a fine of up to $500 per offense, with each week of continued occupancy or construction treated as a new offense. The Zoning Administrator can also withhold a certificate of occupancy for the structure until a special use permit is obtained.

Frequently Asked Questions

Can I build an accessory dwelling unit on my property in unincorporated Macon County?

Not as a matter of right. Section 155.051(B)(11) blocks guest houses, servants' quarters, and apartments as accessory buildings, so you need a special use permit approved by the Board of Appeals before adding a second living unit.

Who reviews a special use permit application for a guest house?

The Administrative Officer refers the petition to the Board of Appeals for a public hearing, and the County Regional Planning Commission and County Health Department submit written recommendations before the Board rules.

How long is a special use permit for an accessory apartment good for?

It becomes void if work is not substantially underway within one year of issuance, and it expires if the approved use stops for more than a year, under § 155.047(C) and (D).

What happens if I build an apartment above my garage without a permit?

You're subject to Macon County's general zoning penalty at § 155.999: up to $500 per offense, with each week the violation continues counted separately, and the county can withhold occupancy approval.

Sources & Official References

[1]Macon County, IL Code of Ordinances (American Legal Publishing)

Other rules in Macon County

Noise Ordinances: Quiet HoursSome Restrictions Noise Ordinances: Construction HoursSome Restrictions Shed & Carport RulesSome Restrictions Noise Ordinances: Barking DogsSome Restrictions Noise Ordinances: Vehicle NoiseFew Restrictions Noise Ordinances: Decibel LimitsSome Restrictions Parking Rules: Commercial & Oversized VehiclesSome Restrictions

All Macon County rules

How Macon County compares: Easiest Cities to Build an ADU·Compare Macon County to another location·View the Illinois accessory structures overview

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