Mercer County, NJ: flood zone, zoning and property lines by address
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Towns in Mercer County: Trenton, Ewing, Princeton.
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 Mercer County has 93 FIRM panels, the newest effective July 2016; 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 Mercer 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 Jersey statewide parcel map (NJ Office of GIS cadastral layer with the MOD-IV tax list), so a Mercer lot shows the same lines the municipal tax maps draw. Mercer County covers about 143,668 acres of land and 2,799 acres of water.
Mapped lines are approximate. The Mercer County Board of Taxation keeps the parcel record (Mercer County website); every county's office is on the state's county boards of taxation list; a licensed surveyor sets the true corners.
Zoning
In New Jersey zoning is set by each municipality, not by the county: in Mercer County, Trenton, Princeton 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 municipal zoning office has the district, the uses it allows and the lot size it needs. The Mercer County website lists the county's municipalities.
ADU and guest houses
The New Jersey Municipal Land Use Law (N.J.S.A. 40:55D) lets each municipality allow an accessory dwelling unit on a lot with a house. Whether a Mercer lot can add one depends on its district; the municipal 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. Mercer County is soil survey area NJ021, Mercer County, New Jersey, last updated August 2026, on Web Soil Survey.
A new or changed septic system in Mercer County needs a permit from the Mercer County health department under the NJDEP septic rules (N.J.A.C. 7:9A), which tests the soil on the lot itself.
Setbacks
Setbacks in Mercer County come from the zoning district: the front, side and rear distances a house must keep. ParcelSheet does not draw setback lines; the municipal zoning office gives them for the lot's district, and Trenton and Princeton for land inside their limits.
Hazards that apply
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a Mercer lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in Mercer 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 Mercer County has 93 panels, the newest effective July 2016. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in Mercer County?
Open the New Jersey map, type the address, and the parcel outline from the county Board of Taxation 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 Mercer County?
Zoning in Mercer County is set by each municipality (such as Trenton, Princeton), not by the county. ParcelSheet shows the use code on the parcel record and names the municipality; the municipal zoning office has the final word.
Can I build an ADU in Mercer County?
The New Jersey Municipal Land Use Law (N.J.S.A. 40:55D) lets each municipality allow an accessory dwelling unit, and each sets its own rules. In Mercer County ask the municipal 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 Mercer County?
Yes. A new or changed septic system in Mercer County needs a permit from the Mercer County health department under the NJDEP septic rules (N.J.A.C. 7:9A). ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area NJ021 (Mercer County, New Jersey).
Next to Mercer County: Burlington County, Hunterdon County, Middlesex County, Monmouth County, Somerset County.
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