Johnson County, IL zoning map, flood zone and property lines by address
Free, no account. Or open the Illinois map and tap a lot.
Towns in Johnson County: Vienna, Goreville.
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 10 FIRM panels covering Johnson County, the newest effective December 2011; 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 Johnson 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 Johnson lot shows the same lines the county supervisor of assessments draws. Johnson County covers about 219,992 acres of land and 3,166 acres of water.
Mapped lines are approximate. The Johnson County supervisor of assessments keeps the parcel record; a licensed surveyor sets the true corners.
Zoning
Johnson County zones its unincorporated land, and Vienna, Goreville each zone the land inside their limits. 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 Johnson 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. Johnson County is soil survey area IL087, Johnson County, Illinois, last updated August 2026, on Web Soil Survey.
A new or changed septic system in Johnson County needs a permit from the Johnson County health department (Illinois Department of Public Health private sewage program; IDPH itself where the county has no health department).
Setbacks
Setbacks in Johnson 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, and Vienna and Goreville for land inside their limits.
Hazards that apply
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a Johnson lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in Johnson County?
Type the address in the box above and ParcelSheet reads FEMA's flood zone at the lot's center. FEMA has 10 flood map panels covering Johnson County, the newest effective December 2011. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in Johnson County?
Open the Illinois map, type the address, and the parcel outline from the Johnson 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 Johnson County?
Zoning in Johnson County is set by the county for unincorporated land and by each city (such as Vienna, Goreville) 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 Johnson 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 Johnson 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 Johnson County?
Yes. A new or changed septic system in Johnson County needs a permit from the Johnson 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 IL087 (Johnson County, Illinois).
What can I build on 5 acres in Johnson County?
Zoning in Johnson County is set by the county for unincorporated land and each city inside its own limits (such as Vienna, Goreville). 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.
What are the residential setbacks in Johnson County (2026)?
Setbacks in Johnson 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.
Next to Johnson County: Massac County, Pope County, Pulaski County, Saline County, Union County, Williamson County.
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