Westchester County, NY: flood zone, zoning and property lines by address
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Towns in Westchester County: Greenburgh, New Rochelle, Mount Vernon.
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 Westchester County has 171 FIRM panels, the newest effective September 2007; 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 Westchester 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 New York State Tax Parcels layer (NYS GIS Program Office, from each county's tax maps), so a Westchester lot shows the same lines the Real Property Tax Services office draws. Westchester County covers about 275,723 acres of land and 44,329 acres of water.
Mapped lines are approximate. The Westchester County Real Property Tax Services office keeps the parcel record; every county's office is on the state's county directors of Real Property Tax Services page; a licensed surveyor sets the true corners.
Zoning
In New York zoning is set by each town, village and city, not by the county: in Westchester County, New Rochelle, Mount Vernon each zone the land inside their limits. ParcelSheet shows the use code on the lot's parcel record and the municipality it sits in; the town, village or city zoning office has the district, the uses it allows and the lot size it needs. The Westchester County website lists the county's municipalities.
ADU and guest houses
New York's zoning enabling laws (Town Law 261, Village Law 7-700 and General City Law 20) lets each town, village and city allow an accessory dwelling unit on a lot with a house. Whether a Westchester lot can add one depends on its district; the town, village or city 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. Westchester County is soil survey area NY119, Westchester County, New York, last updated September 2026, on Web Soil Survey.
A new or changed septic system in Westchester County needs a permit from the Westchester County health department, or the NYS Department of Health district office where the county has none, which tests the soil on the lot itself.
Setbacks
Setbacks in Westchester County come from the zoning district: the front, side and rear distances a house must keep. ParcelSheet does not draw setback lines; the town, village or city zoning office gives them for the lot's district, and New Rochelle and Mount Vernon for land inside their limits.
Hazards that apply
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a Westchester lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in Westchester 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 Westchester County has 171 panels, the newest effective September 2007. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in Westchester County?
Open the New York map, type the address, and the parcel outline from the county Real Property Tax Services office 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 Westchester County?
Zoning in Westchester County is set by each town, village and city (such as New Rochelle, Mount Vernon), not by the county. ParcelSheet shows the use code on the parcel record and names the municipality; the town, village or city zoning office has the final word.
Can I build an ADU in Westchester County?
New York's zoning enabling laws (Town Law 261, Village Law 7-700 and General City Law 20) lets each town, village and city allow an accessory dwelling unit, and each sets its own rules. In Westchester County ask the town, village or city 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 Westchester County?
Yes. A new or changed septic system in Westchester County needs a permit from the Westchester County health department, or the NYS Department of Health district office where the county has none. ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area NY119 (Westchester County, New York).
Next to Westchester County: Bronx County, Nassau County, Putnam County, Rockland County.
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