Nassau & Suffolk Counties, New York Nassau grievance deadline March 31, 2027Nassau grievance deadline Mar 31
Long Island Property Tax
Assessments

Nassau County Department of Assessment

The Nassau County Department of Assessment values every parcel in the county — 424,058 parcels on the 2025 roll, including 384,657 residential homes. Below is a plain-English walkthrough of how Nassau assessments work, how to find yours, and how (and when) to challenge it.

Last verified 4 min read

Nassau parcels
424,058
2025 roll
Residential parcels
384,657
Towns + villages
78
each with its own RAR
Median home value
$506,000
2025 roll
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Look up your Nassau assessment

Type a Nassau address to see the assessed value, exemptions on file, school district, and estimated tax bill. We pull from the official 2025 assessment roll.

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What the Nassau County Department of Assessment does

The Nassau County Department of Assessment (often called “the Assessor”) is responsible for declaring the value of every taxable parcel in Nassau County. That declared value becomes the basis for your county, town, school, and (if applicable) village tax bill.

The Department publishes a tentative assessment roll on January 2 each year showing the new values for the upcoming tax cycle. Homeowners can file a grievance with the Nassau County Assessment Review Commission (ARC) between January 2 and the March deadline. The final roll is published April 1.

The Department does NOT handle: deeds and mortgages (that’s the Nassau County Clerk), tax payments (Nassau County Treasurer + each town receiver), or STAR check delivery (NY State Department of Taxation and Finance). It only sets values.

How Nassau assessment math actually works

Nassau uses what assessors call a “fractional” level of assessment (LOA). Instead of assessing your home at its full market value, they assess it at a small fraction — and then apply a much higher tax rate to that smaller number. The math works out to the same bill, but it makes the numbers look strange:

Example (median Nassau home):
· Full market value (assessor’s declared value): $506,000
· Assessed value (what gets multiplied by tax rate): $536
· The fraction: roughly 0.106% (varies by town and year)

Important: this is the median across Nassau. The exact ratio differs by town and incorporated village. The official NY State ORPTS Equalization Rates page lists the current Residential Assessment Ratio (RAR) and equalization rate for each Nassau municipality.

How Nassau differs from Suffolk

  • Reassessment cycle — Nassau reassesses on a fixed cycle (currently every 4 years between county-wide reassessments, with annual roll updates). Suffolk towns each set their own cycle — some haven’t reassessed comprehensively in decades.
  • Grievance is county-level — In Nassau, all grievances go through the Assessment Review Commission (ARC) at the county. In Suffolk, you file with each town’s individual Board of Assessment Review (BAR).
  • Filing window — Nassau ARC: January 2 through March for the next cycle. Suffolk: third Tuesday in May is “Grievance Day” for each town.
  • Two-year lag — Nassau has roughly a two-year lag: a grievance filed by March 31, 2026 affects the 2027/28 tax bills (mailed October 2027 for school + January 2028 for general).

How to look up your own Nassau assessment

Three ways, in order of ease:

  1. Use our search (at the top of this page). Type your address — we show the assessed value, full market value, school district, current exemptions, and estimated tax bill on one screen.
  2. My Nassau Property (mynassauproperty.com) — the official Nassau Department of Assessment site. Authoritative but harder to read.
  3. Your most recent tax bill shows the assessed value at the top, along with the Section / Block / Lot identifier. We have a line-by-line guide for those.

When and how to challenge a Nassau assessment

If you believe Nassau has assessed your home too high relative to comparable recent sales, you have the right to file a grievance with the Assessment Review Commission (ARC). This is free and you don’t need an attorney, though many homeowners use one.

The process:

  1. Review the tentative roll published January 2.
  2. Gather evidence — recent sale prices of comparable Nassau homes (same town, similar size, similar condition). Three to five comps is typical.
  3. File Form RP-524 (or the online equivalent) with ARC by the published deadline.
  4. ARC reviews through the spring/summer and issues a decision.
  5. If denied or unsatisfied, file a Small Claims Assessment Review (SCAR) petition in Nassau County Supreme Court within 30 days.

Full walkthrough: Nassau County tax grievance guide.

Frequently asked questions

How do I contact the Nassau County Department of Assessment?
The Nassau County Department of Assessment can be reached at 516-571-1500. Their physical office is at 240 Old Country Road, Mineola, NY 11501. For the most up-to-date contact and form information, visit nassaucountyny.gov/agencies/Assessment.
What is Nassau County’s Level of Assessment (LOA)?
Nassau publishes a Level of Assessment per municipality (town and each incorporated village have their own). For grievance purposes, ARC has historically used a county-wide level around 0.66% — meaning your assessed value should be roughly 0.66% of true market value. Specific RARs are published annually by NY State ORPTS at tax.ny.gov. Check the latest figure for your specific town or village before filing a grievance.
When is the Nassau ARC grievance deadline?
Nassau ARC accepts grievances each year from January 2 through the deadline (typically March 1, but it has been extended in recent cycles — for example, the 2027/28 cycle was extended to March 31, 2026). Check nassaucountyny.gov/agencies/ARC for the current cycle’s exact deadline.
What’s the difference between assessed value, full market value, and taxable value?
Full market value is what the assessor thinks the home would sell for. Assessed value is full market value multiplied by the town’s Level of Assessment (a small fraction in Nassau). Taxable value is assessed value minus exemptions (STAR, Senior, Veteran, etc.). The tax rate is applied to the taxable value to compute your bill.
Why is my Nassau assessment so different from my home’s sale price?
Nassau assessments lag market reality, sometimes substantially. Nassau’s assessor sets the value as of January 2 of each cycle, so a home that has appreciated since the last reassessment will often show an assessed value well below recent sale prices. This is normal — the assessment is a snapshot in time, not a real-time appraisal.
Does the Nassau Department of Assessment send my tax bill?
No. The Department only sets values. Your school tax bill is mailed by your school district’s receiver in October. Your general tax bill (county + town) is mailed by your town’s Receiver of Taxes in January. Incorporated villages send a separate village tax bill in June.
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Sources and citations

Last verified October 7, 2026. Tax rules change; we re-check every page each quarter.

Educational content and estimates only, not legal, tax or financial advice. Verify with your county or town receiver, an attorney or a CPA before making financial decisions.