Compare county building requirements and land costs
| County | Building code | Dwelling permit | Fees | Min. lot (rural zoning) | Septic | Growth 2020–25 | Land (asking avg/ac, Oct 2026) | Page |
|---|---|---|---|---|---|---|---|---|
| Franklin | 2021 IRC, eff. Apr 23, 2024; inspected | Yes | $25 app + sq-ft fee + $350 escrow (refunded) | confirm | County ordinance (eff. Oct 2025), via Building Dept | +3.3% | ~$34,700 | Franklin |
| Jefferson | 2015 IRC per published code (confirm edition) | Yes | On cost, valued ≥ $120/sq ft | RA-5: 5 acres | County | +2.9% | ~$37,400 | Jefferson |
| Warren | None | Yes — structure permit, septic first | $150 + $200 septic + $10 sticker | AG: 3 acres | County Sanitarian | +9.8% | ~$36,500 | Warren |
| Lincoln | None | None (floodplain only) | — | None | Health Dept | +11.9% | ~$58,900 | Lincoln |
| St. Charles | 2021 county code; inspected | Yes | confirm | A: 5 acres; 800 sq ft min. dwelling | County private sewage code | +5.2% | — | St. Charles |
All five participate in the National Flood Insurance Program and require a floodplain development permit in mapped areas. Design values where published (Franklin, St. Charles): Seismic Design Category C, 30-inch frost, 105–107 mph wind, 20 psf snow. Download the matrix as a CSV: county-matrix.csv.
St. Louis County (unincorporated)
St. Louis County enforces a county building code through Public Works; its website blocked our reading of the current code edition, zoning minimums and permit rules at this update, and most of the county's land is inside its nearly ninety municipalities and their covenants. We build in unincorporated St. Louis County on a parcel-by-parcel check.
Metro East (Illinois)
Monroe and Madison counties have building departments and require permits (St. Clair County not yet checked). What we have read so far: Monroe County's posted code adopts the 2006 IBC/IRC (confirm current), charges $5 per $1,000 of value, and requires a Bi-County Health Department septic and water permit before the building permit; Madison County charges $0.15 per square foot, requires a 620-square-foot minimum single-family dwelling, allows standing-seam metal roofs in agricultural and residential districts but states "tin roofs are not" allowed, and requires finished floors two feet above base flood elevation. A Metro East page is next in line; until then, Illinois parcels are quoted after a county check.
Beyond the ring
Washington, Ste. Genevieve, Gasconade, Montgomery and Pike counties: quoted case by case, with the same county-first process.