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Single Family ResidenceResidential
$825,006$456 / ft²
TopHap EstimateOur estimate of what this home would sell for today, based on nearby sales, the home's size and features, and local price trends. It is a starting point, not an appraisal.· confidence 92How well the pricing models agreed with each other on this home. Higher means the estimate rests on stronger, more consistent data.· as of Sep 24, 2026

21 KNOLLWOOD RD

ROCKVILLE CENTRE, NY 11570
2.5
Baths
1,811 ft²
Living AreaTotal finished area of the structures, from county records. Some counties include shared space like hallways or a building gym, so it may not match a listing.
0.14 ac
Lot SizeThe size of the land the home sits on, from county records.
1935
Year BuiltThe year the home was originally built, according to county records.
1
StoriesHow many floors the home has above ground.
6
RoomsThe total room count in county records. Counties differ on which rooms they count, so compare it loosely.
1
ParkingThe number of parking spaces on the property, including the garage.

Valuation

$825K
$759K low$891K high

Tax & Assessment

Property TaxThe property tax billed for this tax year. It usually pays for schools, roads, and local services.$14,825 (2025)
Assessed ValueThe value the county assigns to this home to calculate property tax. It is often lower than what the home would sell for.$660 (2026)
Assessed LandThe share of the county's assessed value that comes from the land itself, not the buildings.$162
Assessed ImprovementsThe share of the county's assessed value that comes from the buildings and other structures on the land.$498
Previous AssessedThe county's assessed value from the year before, useful for seeing how the assessment changed.$660
Assessor Market ValueThe county assessor's own opinion of market value. It is separate from our estimate and updates on the county's schedule.$660,000

Property Facts

Property TypeThe broad category the county puts this property in, such as residential or commercial.Single Family Residence
StyleThe architectural style of the home, such as ranch or colonial.Cape Cod
CountyNASSAU
Lot (acres)The size of the land the home sits on, from county records.0.14
ConstructionThe main material the home's frame and walls are built from.Frame (Unspecified)
RoofThe main material covering the roof, such as asphalt shingle or tile.Slate
HeatingThe type of heating system in the home.Central
CoolingThe type of cooling or air conditioning in the home.Central
FireplaceWhether the home has a fireplace, and what kind.Yes
GarageWhether the property has a garage, and details like whether it is attached to the home.Garage, Attached
PoolWhether the property has a pool, and what kind, such as in-ground.No
FeaturesExtra features found in county records. Records are not complete everywhere, so a missing feature does not always mean the home lacks it.Porch · 88 ft²

Neighborhood · ZIP 11570These are comparison scores, not percentages. 100 equals the national average, so 150 means about 50% above average.

CrimeLocal crime compared with the rest of the country, where 100 is average. It reflects things like population density, income, and how crime gets reported.82
Air pollutionOverall air pollution compared with the rest of the country, where 100 is average. Lower is cleaner.112
EarthquakeEarthquake risk and likely building damage compared with the rest of the country, where 100 is average. Scores can run far above 100.91

Index scale: 100 = US average (tick). Lower is better.

Homes occupiedThe share of homes here that someone lives in. The rest sit empty, including vacation and for-sale homes.97%
Bachelor's or higherThe share of adults 25 and older whose highest degree is a bachelor's degree.32%
Poverty rateThe share of people whose household income falls below the federal poverty line, which varies by family size.4.6%
UnemploymentThe share of men 16 and older who are out of work and actively looking. Only men are counted in this figure.1.0%
PopulationHow many people live in this area.28,370
DensityPeople per square mile. Higher numbers mean a more crowded, urban area.7,589 / mi²
Median incomeThe middle household income here — half of households earn more, half earn less.$144,451
Average incomeThe average household income. It runs higher than the median when a few high earners pull it up.$184,571
Average tempThe average temperature here across a full year.54°F
Annual precipHow much rain and melted snow falls here in a typical year.49 in
SunshineThe share of daylight hours that get direct sun in a typical year, counting cloud cover.56%

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Data by ATTOM. Valuations are automated estimates, not appraisals. Photos from Google Street View and may not depict the current property state.

How this home compares

21 Knollwood Rd measured against every home in its neighborhood, its ZIP code and its county, using county assessor records refreshed nightly. A home can stand out in one of those areas and look ordinary in another, because each one holds a different mix of homes.

  • Worth less than 78% of homes in Rockville Centre 11570
  • Costs less per square foot than 72% of homes in Nassau County
  • Smaller than 66% of homes in Rockville Centre 11570
  • Has a smaller lot than 77% of homes in Rockville Centre 11570
  • Older than 81% of homes in Nassau County

What homes are worth in Rockville Centre 11570

Each bar is how many homes fall in that price range. The marker is this home.

This home
$614K$1.6M

This home is worth more than 22% of homes in Rockville Centre 11570.

How it measures up in Rockville Centre 11570

The dot is this home. The mark in the middle is the typical home in Rockville Centre 11570.

Estimated value$825,006
CheaperTypical $968,335Pricier

Pricier than 22% of homes nearby

Price per ft²$456
CheaperTypical $483Pricier

Pricier than 33% of homes nearby

Living area1,811 ft²
SmallerTypical 2,060 ft²Bigger

Bigger than 34% of homes nearby

Lot size0.14 ac
SmallerTypical 0.16 acBigger

Bigger than 23% of homes nearby

Year built1935
OlderTypical 1935Newer

Newer than 51% of homes nearby

How 21 Knollwood Rd ranks against every home in each area.
MeasureThis homeRockville Centre 11570Nassau County
Estimated valuepricier than$825,00622% of homes49% of homes
Price per ft²pricier than$45633% of homes28% of homes
Living areabigger than1,811 ft²34% of homes54% of homes
Lot sizebigger than0.14 ac23% of homes29% of homes
Year builtnewer than193551% of homes19% of homes

About 21 Knollwood Rd

How much is 21 Knollwood Rd, Rockville Centre, NY worth?

The TopHap Estimate for 21 Knollwood Rd, Rockville Centre, NY is $825,006 as of Sep 24, 2026. The likely range is $758,541 to $891,471. The estimate is modelled from recorded sales, assessments and the property's own characteristics — it is not an appraisal.

When did 21 Knollwood Rd, Rockville Centre, NY last sell?

21 Knollwood Rd, Rockville Centre, NY last sold on Jan 1, 1900, according to the county's recorded deed.

How big is 21 Knollwood Rd, Rockville Centre, NY?

21 Knollwood Rd, Rockville Centre, NY has 2.5 bathrooms, 1,811 square feet of living space and a 0.14-acre lot.

When was 21 Knollwood Rd, Rockville Centre, NY built?

21 Knollwood Rd, Rockville Centre, NY was built in 1935, making it 91 years old. It is a cape cod home. The building has 1 story.

How does 21 Knollwood Rd, Rockville Centre, NY compare to other homes in Rockville Centre 11570?

Among the 6,982 homes in Rockville Centre 11570, it is worth more than 22% of them ($825,006 against a typical $968,335), its price per square foot is higher than 33% of them ($456 against a typical $483), it is bigger than 34% of them (1,811 ft² against a typical 2,060 ft²), its lot is bigger than 23% of them (0.14 ac against a typical 0.16 ac) and it is newer than 51% of them (1935 against a typical 1935). Measured against all of Nassau County, it is worth more than 49% of homes there. These shares are recounted nightly from the full county assessor record for each area, not from active listings.

What are the property taxes on 21 Knollwood Rd, Rockville Centre, NY?

The 2025 property tax bill for 21 Knollwood Rd, Rockville Centre, NY was $14,825. The county assessed it at $660.

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