Nassau County home values keep setting records. That's good news if you're selling. It's a different story if you're staying put, because the same strength that lifts your equity also lifts the number the county taxes you on.
The headline numbers
OneKey MLS reported a record median single-family sale price of $890,000 in Nassau County in May 2026 — up 9.9% from a year earlier.
This is a supply story
Prices aren't climbing because Long Island suddenly became more desirable. They're climbing because almost nothing is for sale.
Nassau inventory sat at just 1,473 homes in February 2026, down 16.6% year over year, with new listings down 23.7%. Owners holding low mortgage rates have little reason to trade them for today's, so they stay put — and the handful of homes that do reach the market get bid up hard.
How that reaches your tax bill
Nassau assesses property on market value. When homes around you sell for records, those sales become the raw material for what the county believes your house is worth — whether or not you changed a single thing about it.
A rising assessment isn't automatically a wrong one. What matters is your position relative to comparable homes nearby. If everything on your street rose and your assessment rose with it, you may be right where you belong. If yours moved more than the block did, that's the gap worth looking at.
Where the model gets your house wrong
Assessments are produced by mass appraisal — statistical models applied across hundreds of thousands of parcels at once. Models are good at neighborhoods and bad at individual houses. They don't know your kitchen is original, that your lot backs onto a commercial parking lot, or that the comparable sale two doors down was a gut renovation and yours is not.
In a fast market, those blind spots widen, because the model is chasing a moving target — and it tends to chase prices up far more eagerly than it walks them back down. The drift runs one direction.
Where we come in
Nassau publishes a new tentative assessment roll each January. Reading that notice and testing it against what comparable homes actually sold for is our job, not yours — it's what we do every January for the people we represent. You don't need to know what to look for, and you don't need to remember to look.
Your home going up in value isn't a problem. Being taxed as though it went up more than it actually did is. If your latest assessment jumped, that's exactly the moment to have the comparison checked, and that's the part we handle for you.