Madison County, IL Building Setbacks & Zoning: Lot Coverage Limits (2026)

Madison County's R-1 through R-4 Single-Family Residential Districts share one set of dimensional standards under § 93.025(B). Division (6) states lot coverage may not exceed 15% of the area of a zoning lot, covered by 'buildings or structures, including accessory buildings.' The same section's division (7) caps the floor area ratio between gross floor area and the zoning lot at 0.3, 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.

The county applies a nearly identical 15% lot-coverage cap in the more rural C Conservation District under § 93.024(B)(6), though that district's floor area ratio, yard depths and three-acre minimum lot size are all larger. Both sections direct applicants to the county's separate fence standards at § 93.080, parking standards, and slope regulations at § 93.063 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.