Madison County, IL Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- Lot coverage cap
- 15% of zoning lot, § 93.025(B)(6)
- Floor area ratio
- 0.3 max, § 93.025(B)(7)
- Accessory structure limit
- 2x first-level floor area of main house
- Applies to
- R-1 through R-4 districts, unincorporated county only
- Conservation District
- Same 15% cap, § 93.024(B)(6)
- Penalty
- $10-$500 per day, § 93.999
Summary
In unincorporated Madison County's R-1 through R-4 single-family districts, Zoning Code § 93.025(B)(6) caps lot coverage at 15% of the zoning lot for all buildings and structures, including accessory buildings, and pairs it with a 0.3 maximum floor area ratio.
(6) Lot coverage. Not more than 15% of the area of a zoning lot may be covered by buildings or structures, including accessory buildings. (7) Maximum floor area ratio. The floor area ratio between gross floor area and zoning lot shall not exceed 0.3. The maximum floor area of accessory structures shall be no greater than two times the first-level floor area of the primary structure.
Full Breakdown
025(B). 3, and further limits accessory structures to no more than twice the first-level floor area of the primary structure. These limits sit alongside the district's other standards: a minimum 40,000-square-foot lot with 150 feet of width at the building line, a 40-foot front yard, 25-foot side yards (40 feet where a side yard adjoins a street), and a 40-foot rear yard. 024(B)(6), though that district's floor area ratio, yard depths and three-acre minimum lot size are all larger. 063 for additional requirements that can affect how much of a lot can actually be built on.
As with every other zoning provision in this code, the 15% cap applies only to unincorporated Madison County; Edwardsville, Alton, Collinsville, Granite City and the county's other cities and villages set their own lot-coverage limits inside their corporate limits.
Violations & Fines
Exceeding the 15% lot-coverage cap or the 0.3 floor area ratio in an R-1 through R-4 district is a zoning code violation under § 93.999, carrying a fine of $10 to $500 with each day of continued noncompliance a separate offense; the county or an affected neighbor may also seek a Circuit Court order to correct or remove the excess construction.
Frequently Asked Questions
How much of my lot can I cover with buildings in unincorporated Madison County?
Does the Conservation District have the same coverage limit?
How big can my detached garage be relative to my house?
Sources & Official References
Other rules in Madison County
Compare Madison County to another location·View the Illinois building setbacks & zoning overview
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