Colusa County, CA zoning map, flood zone and property lines by address
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Towns in Colusa County: Colusa, Williams, Arbuckle.
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 Colusa County has 60 FIRM panels, the newest effective March 2024; 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 Colusa 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 California county parcel layers (each county publishes its own), so a Colusa lot shows the same lines the county assessor draws. Colusa County covers about 736,409 acres of land and 3,650 acres of water.
Mapped lines are approximate. The Colusa County assessor keeps the parcel record (Colusa County website); a licensed surveyor sets the true corners.
Zoning
Colusa County zones its unincorporated land, and Colusa, Williams each zone the land inside their limits. ParcelSheet shows the use the county assessor lists for the lot and links the county planning department for the district, the uses it allows and the lot size it needs.
ADU and guest houses
Under California's Planning and Zoning Law (Government Code Title 7, Division 1, starting at section 65000), local governments can allow an accessory dwelling unit on a lot with a house. Whether a Colusa lot can add one depends on its district; the county planning department 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. Colusa County is soil survey area CA011, Colusa County, California, last updated September 2026, on Web Soil Survey.
A new or changed septic system in Colusa County needs a permit from the Colusa County environmental health department (under the State Water Resources Control Board OWTS Policy).
Setbacks
Setbacks in Colusa 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 Colusa and Williams for land inside their limits.
Hazards that apply
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a Colusa lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in Colusa 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 Colusa County has 60 panels, the newest effective March 2024. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in Colusa County?
Open the California map, type the address, and the parcel outline from the Colusa 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 Colusa County?
Zoning in Colusa County is set by the county for unincorporated land and by each city (such as Colusa, Williams) 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 Colusa County?
Under California's Planning and Zoning Law (Government Code Title 7, Division 1, starting at section 65000), counties and cities can allow an accessory dwelling unit, and each sets its own rules. In Colusa 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 Colusa County?
Yes. A new or changed septic system in Colusa County needs a permit from the Colusa County environmental health department (under the State Water Resources Control Board OWTS Policy). ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area CA011 (Colusa County, California).
What can I build on 5 acres in Colusa County?
Zoning in Colusa County is set by the county for unincorporated land and each city inside its own limits (such as Colusa, Williams). 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 Colusa County website.
What are the residential setbacks in Colusa County (2026)?
Setbacks in Colusa 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 Colusa County website.
Next to Colusa County: Butte County, Glenn County, Lake County, Sutter County, Yolo County.
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