St. Clair County, IL zoning map, flood zone and property lines by address
Free, no account. Or open the Illinois map and tap a lot.
Flood zone by address
ParcelSheet reads FEMA's National Flood Hazard Layer at the lot: the zone, whether it is a high risk area where lenders ask for flood insurance, and the base flood elevation where FEMA lists one. FEMA has 28 FIRM panels covering St. Clair County, the newest effective August 2025; no coastal V zones are mapped in it.
The official panel and any Letter of Map Amendment are at FEMA's Map Service Center. An elevation certificate for a St. Clair house comes from a licensed surveyor and is often on file with the county or city building office.
Property lines
The parcel outline, parcel number and mapped size come from the Illinois county parcel layers (each county publishes its own), so a St. Clair lot shows the same lines the county supervisor of assessments draws. St. Clair County covers about 420,959 acres of land and 10,331 acres of water.
Mapped lines are approximate. The St. Clair County supervisor of assessments keeps the parcel record (St. Clair County website); a licensed surveyor sets the true corners.
Zoning
St. Clair County zones its unincorporated land. ParcelSheet shows the use the county supervisor of assessments lists for the lot and links the county zoning office for the district, the uses it allows and the lot size it needs.
ADU and guest houses
Under Illinois's county zoning law (Counties Code, 55 ILCS 5/5-12001 and following), local governments can allow an accessory dwelling unit on a lot with a house. Whether a St. Clair lot can add one depends on its district; the county zoning office has the rule. ParcelSheet shows the mapped lot size and the ground's slope, the first two things the question turns on.
Septic and soil
ParcelSheet reads the USDA soil survey at the lot: the soil's name, its septic absorption rating and whether it is prime farmland. St. Clair County is soil survey area IL163, St. Clair County, Illinois, last updated August 2026, on Web Soil Survey.
A new or changed septic system in St. Clair County needs a permit from the St. Clair County health department (Illinois Department of Public Health private sewage program; IDPH itself where the county has no health department).
Setbacks
Setbacks in St. Clair County come from the zoning district: the front, side and rear distances a house must keep. ParcelSheet does not draw setback lines; the county zoning office gives them for the lot's district.
Hazards that apply
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a St. Clair lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in St. Clair County?
Type the address in the box above and ParcelSheet reads FEMA's flood zone at the lot's center. FEMA has 28 flood map panels covering St. Clair County, the newest effective August 2025. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in St. Clair County?
Open the Illinois map, type the address, and the parcel outline from the St. Clair County supervisor of assessments shows on the map with its parcel number and mapped size. Mapped lines are approximate; only a licensed surveyor sets the true corners.
What is my property zoned in St. Clair County?
Zoning in St. Clair County is set by the county for unincorporated land and by each city inside its own limits. ParcelSheet shows the use code the county supervisor of assessments lists and links the office that sets the zoning; the planning office has the final word.
Can I build an ADU in St. Clair County?
Under Illinois's county zoning law (Counties Code, 55 ILCS 5/5-12001 and following), counties and cities can allow an accessory dwelling unit, and each sets its own rules. In St. Clair County ask the zoning office for the lot's district first; ParcelSheet shows the lot size as mapped so you can see the room you have.
Do I need a septic permit in St. Clair County?
Yes. A new or changed septic system in St. Clair County needs a permit from the St. Clair County health department (Illinois Department of Public Health private sewage program; IDPH itself where the county has no health department). ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area IL163 (St. Clair County, Illinois).
What can I build on 5 acres in St. Clair County?
Zoning in St. Clair County is set by the county for unincorporated land and each city inside its own limits. The zoning district decides the uses, how many homes and the smallest lot it allows on 5 acres. ParcelSheet shows the lot size as mapped and the use code on the parcel record; the planning office has the district and its rules. See the St. Clair County website.
What are the residential setbacks in St. Clair County (2026)?
Setbacks in St. Clair County come from the zoning code of the county, or of the city when the lot is inside city limits: the front, side and rear distances depend on the lot's district. ParcelSheet does not draw setback lines or give a number it did not read; the zoning office gives them for the district. See the St. Clair County website.
Next to St. Clair County: Clinton County, Madison County, Monroe County, Randolph County.
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