Jefferson County, MO zoning map, flood zone and property lines by address
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Towns in Jefferson County: Arnold, Festus, Murphy.
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's countywide study for Jefferson County has 174 FIRM panels, the newest effective October 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 Jefferson 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 Missouri county parcel layers (each county publishes its own), so a Jefferson lot shows the same lines the county assessor draws. Jefferson County covers about 419,867 acres of land and 5,003 acres of water.
Mapped lines are approximate. The Jefferson County assessor keeps the parcel record (Jefferson County website); a licensed surveyor sets the true corners.
Zoning
Jefferson County zones its unincorporated land, and Arnold, Festus each zone the land inside their limits. ParcelSheet shows the use the county assessor lists for the lot and links the county planning and zoning office for the district, the uses it allows and the lot size it needs.
ADU and guest houses
Under Missouri's county planning and zoning law (Revised Statutes of Missouri Chapter 64), local governments can allow an accessory dwelling unit on a lot with a house. Whether a Jefferson lot can add one depends on its district; the county planning and 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. Jefferson County is soil survey area MO099, Jefferson County, Missouri, last updated August 2026, on Web Soil Survey.
A new or changed septic system in Jefferson County needs a permit from the Jefferson County health department, or the county's other designated onsite authority (Missouri Department of Health and Senior Services onsite wastewater program).
Setbacks
Setbacks in Jefferson 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 Arnold and Festus for land inside their limits.
Hazards that apply
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a Jefferson lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in Jefferson County?
Type the address in the box above and ParcelSheet reads FEMA's flood zone at the lot's center. FEMA's countywide flood map for Jefferson County has 174 panels, the newest effective October 2025. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in Jefferson County?
Open the Missouri map, type the address, and the parcel outline from the Jefferson County assessor 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 Jefferson County?
Zoning in Jefferson County is set by the county for unincorporated land and by each city (such as Arnold, Festus) inside its own limits. ParcelSheet shows the use code the county assessor lists and links the office that sets the zoning; the planning office has the final word.
Can I build an ADU in Jefferson County?
Under Missouri's county planning and zoning law (Revised Statutes of Missouri Chapter 64), counties and cities can allow an accessory dwelling unit, and each sets its own rules. In Jefferson 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 Jefferson County?
Yes. A new or changed septic system in Jefferson County needs a permit from the Jefferson County health department, or the county's other designated onsite authority (Missouri Department of Health and Senior Services onsite wastewater program). ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area MO099 (Jefferson County, Missouri).
What can I build on 5 acres in Jefferson County?
Zoning in Jefferson County is set by the county for unincorporated land and each city inside its own limits (such as Arnold, Festus). 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 Jefferson County website.
What are the residential setbacks in Jefferson County (2026)?
Setbacks in Jefferson 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 Jefferson County website.
Next to Jefferson County: Franklin County, Ste. Genevieve County, St. Francois County, St. Louis County, Washington County.
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