Mason County, WA zoning map, flood zone and property lines by address
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Towns in Mason County: Shelton, Belfair, Allyn.
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 Mason County has 75 FIRM panels, the newest effective June 2019; coastal V zones, where waves add to the flood, are mapped along its shore.
The official panel and any Letter of Map Amendment are at FEMA's Map Service Center. An elevation certificate for a Mason 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 Washington Technology Solutions (WaTech), statewide parcels from the counties, so a Mason lot shows the same lines the county assessor draws. Mason County covers about 614,121 acres of land and 58,546 acres of water.
Mapped lines are approximate. The Mason County assessor keeps the parcel record (Mason County website); a licensed surveyor sets the true corners.
Zoning
Mason County zones its unincorporated land, and Shelton zones the land inside its 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 Washington's Planning Enabling Act and Growth Management Act (Revised Code of Washington Chapters 36.70 and 36.70A), local governments can allow an accessory dwelling unit on a lot with a house. Whether a Mason 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. Mason County is soil survey area WA645, Mason County, Washington, last updated September 2026, on Web Soil Survey.
A new or changed septic system in Mason County needs a permit from the Mason County health department (local health jurisdiction, under Washington State Department of Health on site sewage rules).
Setbacks
Setbacks in Mason 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 Shelton for land inside its limits.
Hazards that apply
- Storm surge. Mason County has coastal V zones on its FEMA map, so storm surge reaches its shore. The county's evacuation zones are on its emergency management site; ParcelSheet shows the FEMA zone and the 3 ft sea level rise map at the lot.
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a Mason lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in Mason 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 Mason County has 75 panels, the newest effective June 2019. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in Mason County?
Open the Washington map, type the address, and the parcel outline from the Mason 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 Mason County?
Zoning in Mason County is set by the county for unincorporated land and by each city (such as Shelton) 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 Mason County?
Under Washington's Planning Enabling Act and Growth Management Act (Revised Code of Washington Chapters 36.70 and 36.70A), counties and cities can allow an accessory dwelling unit, and each sets its own rules. In Mason 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 Mason County?
Yes. A new or changed septic system in Mason County needs a permit from the Mason County health department (local health jurisdiction, under Washington State Department of Health on site sewage rules). ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area WA645 (Mason County, Washington).
What can I build on 5 acres in Mason County?
Zoning in Mason County is set by the county for unincorporated land and each city inside its own limits (such as Shelton). 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 Mason County website.
What are the residential setbacks in Mason County (2026)?
Setbacks in Mason 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 Mason County website.
Next to Mason County: Grays Harbor County, Jefferson County, Kitsap County, Pierce County, Thurston County.
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