Updated May 2026
Flood Risk in Nassau, NY
Nassau, NY has a Flood Risk Score of 25/100 (Grade B), ranking #54 of 3,277 counties nationwide. The risk level is Moderate. There have been 373 NFIP flood-insurance claims totaling $7,338,653 in payouts, with 16 federal disaster declarations on record.
Key Data
What the Grade Means Here
Nassau carries a B grade — modest but non-trivial flood risk. With a composite score of 25 and 373 NFIP claims on file, the county sits in the second-safest tier of the U.S. distribution (rank #54 of 3,277). Most insured loss here clusters in localized low-elevation neighborhoods or river-adjacent corridors rather than across the whole county.
Within New York, Nassau runs 12 points above the state average composite score of 13 — meaningfully more flood-exposed than the typical county in the state. Rank: #2 of 63. The full New York state profile shows how every county within the state compares.
What's Driving the Risk Score?
The single biggest driver of the composite score in this county is year-over-year trend (15% of the formula, factor score 100). For Nassau, that means the year-over-year trend in flood losses is contributing meaningfully — this is a county where loss has been climbing in recent years, not just historically high.
The trend factor is high (100 of 100), meaning flood losses have been accelerating sharply in this county. That is the single most actionable signal in the score — recent risk is meaningfully greater than the long-run average suggests.
Score Breakdown
| Factor | Score | Weight |
|---|---|---|
| Claims Density | 3 | 40% |
| Disaster Frequency | 34 | 25% |
| Claim Severity | 1 | 20% |
| Year-over-Year Trend | 100 | 15% |
How This Score Is Calculated
The composite is a weighted average of four FEMA-derived factors. Source data comes from the public FEMA flood-mapping program via the OpenFEMA API. For property-level decisions, layer this with the parcel's FEMA Flood Insurance Rate Map zone and recent crest readings from USGS Water Data. Full math: methodology page.
Frequently Asked Questions
What is the flood risk in Nassau, NY?
Nassau, NY has a Flood Risk Score of 25/100 (Grade B), ranking #54 of 3,277 counties nationwide. The risk level is Moderate. There have been 373 NFIP flood-insurance claims totaling $7,338,653 in payouts, with 16 federal disaster declarations on record.
Is flood insurance required in Nassau?
Federal law requires flood insurance for any property in a Special Flood Hazard Area (FEMA Zone A or V) financed by a federally regulated lender. Nassau's county-wide composite score is 25 (Grade B), which is a county aggregate — your specific parcel's flood-zone designation comes from the FEMA Flood Insurance Rate Map (FIRM) at fema.gov/flood-maps. Even when not legally required, NFIP coverage is often available for a few hundred dollars a year in moderate- and low-risk zones, and FEMA reports more than 25% of all NFIP claims come from outside high-risk zones.
What is driving the flood risk score in Nassau?
The single biggest driver of the composite score in this county is year-over-year trend (15% of the formula, factor score 100). For Nassau, that means the year-over-year trend in flood losses is contributing meaningfully — this is a county where loss has been climbing in recent years, not just historically high.
Is flood risk increasing or decreasing in Nassau?
The trend factor is high (100 of 100), meaning flood losses have been accelerating sharply in this county. That is the single most actionable signal in the score — recent risk is meaningfully greater than the long-run average suggests.
How does Nassau compare to other counties in New York?
Within New York, Nassau runs 12 points above the state average composite score of 13 — meaningfully more flood-exposed than the typical county in the state. Rank: #2 of 63.
Where does this data come from?
Every figure on this page comes from FEMA's public OpenFEMA API — the DisasterDeclarationsSummaries v2 endpoint (federally declared flood-related disasters) and the FimaNfipClaims endpoint (individual NFIP flood-insurance claims aggregated by county FIPS code). Both are public-domain U.S. government work. Real-time stream-gauge readings that complement these federal aggregates live at USGS Water Data. Last updated 2026-05-16.
Nassau, NY has a Flood Risk Score of 25/100 (Grade B), ranking #54 of 3,277 counties nationwide. The risk level is Moderate. There have been 373 NFIP flood-insurance claims totaling $7,338,653 in payouts, with 16 federal disaster declarations on record.
The data source behind this answer is FEMA OpenFEMA datasets including the National Flood Hazard Layer and NFIP claims. Every figure on the page traces back to that source; the methodology page describes the inputs and the refresh cadence in full detail.
A practical caveat: the headline answer above reflects the most recent FEMA OpenFEMA datasets including the National Flood Hazard Layer and NFIP claims vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.