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Single Family ResidenceResidential
$440,322$279 / 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 Aug 30, 2026
Last sold for $189,000 on Feb 28, 1994

21 S WILLIAM ST

MOUNT PROSPECT, IL 60056
4
Beds
2 / 1
Baths
1,581 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.
0.21 ac
Lot SizeThe size of the land the home sits on, from county records.
1941
Year BuiltThe year the home was originally built, according to county records.
2
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

$440K
$405K low$475K high
Last SaleThe most recent sale price and date from the recorded deed. Transfers between family members or companies may not reflect market value.$189,000 · Feb 28, 1994

Tax & Assessment

Property TaxThe property tax billed for this tax year. It usually pays for schools, roads, and local services.$9,104 (2023)
Assessed ValueThe value the county assigns to this home to calculate property tax. It is often lower than what the home would sell for.$36,000 (2024)
Assessed LandThe share of the county's assessed value that comes from the land itself, not the buildings.$8,525
Assessed ImprovementsThe share of the county's assessed value that comes from the buildings and other structures on the land.$27,475
Previous AssessedThe county's assessed value from the year before, useful for seeing how the assessment changed.$35,999
Assessor Market ValueThe county assessor's own opinion of market value. It is separate from our estimate and updates on the county's schedule.$360,000

Climate Risk

Overall riskThe average of the five hazard scores below, on a 0 to 100 scale. Higher means greater projected risk over the coming decades.34
1
FloodProjected flooding risk from rivers, heavy rain, and storm surge, scored 0 to 100. Higher is riskier.
1
WildfireProjected wildfire risk, scored 0 to 100, based on how much land burns in a typical year. Higher is riskier.
62
HeatProjected heat risk, scored 0 to 100, based on how many extremely hot days a year are expected. Higher is riskier.
65
StormProjected risk from heavy rainstorms, scored 0 to 100, based on how often extreme rainfall is expected. Higher is riskier.
45
DroughtProjected water shortage risk, scored 0 to 100. Higher means more strain on the local water supply.

Scores 0–100; higher = greater projected risk.

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.Old Style
CountyCook
Lot (acres)The size of the land the home sits on, from county records.0.21
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.Composition Shingle
HeatingThe type of heating system in the home.Forced Air
CoolingThe type of cooling or air conditioning in the home.None
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, Detached

Assigned SchoolsThe public schools this address is zoned for. Boundaries change, so confirm with the district before you count on it.

M
Lincoln Middle SchoolB+
Middle · Grades 6–8 · 1.1 mi
H
Prospect High SchoolA+
High · Grades 9–12 · 1.4 mi
E
Westbrook Early Learning Center
Elementary · Grades PK–1 · 1.6 mi

District: Mount Prospect School District 57

Neighborhood · ZIP 60056These 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.59
Air pollutionOverall air pollution compared with the rest of the country, where 100 is average. Lower is cleaner.124
EarthquakeEarthquake risk and likely building damage compared with the rest of the country, where 100 is average. Scores can run far above 100.43

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.96%
Bachelor's or higherThe share of adults 25 and older whose highest degree is a bachelor's degree.31%
Poverty rateThe share of people whose household income falls below the federal poverty line, which varies by family size.4.7%
UnemploymentThe share of men 16 and older who are out of work and actively looking. Only men are counted in this figure.1.8%
PopulationHow many people live in this area.56,070
DensityPeople per square mile. Higher numbers mean a more crowded, urban area.5,043 / mi²
Median incomeThe middle household income here — half of households earn more, half earn less.$99,966
Average incomeThe average household income. It runs higher than the median when a few high earners pull it up.$121,404
Average tempThe average temperature here across a full year.49°F
Annual precipHow much rain and melted snow falls here in a typical year.37 in
SunshineThe share of daylight hours that get direct sun in a typical year, counting cloud cover.54%

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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 S William St 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 more than 70% of homes in Cook County
  • Has a bigger lot than 65% of homes in Cook County
  • Older than 97% of homes in Mount Prospect 60056

What homes are worth in Mount Prospect 60056

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

This home
$158K$835K

This home is worth more than 52% of homes in Mount Prospect 60056.

How it measures up in Mount Prospect 60056

The dot is this home. The mark in the middle is the typical home in Mount Prospect 60056.

Estimated value$440,322
CheaperTypical $437,185Pricier

Pricier than 52% of homes nearby

Price per ft²$279
CheaperTypical $289Pricier

Pricier than 43% of homes nearby

Living area1,581 ft²
SmallerTypical 1,475 ft²Bigger

Bigger than 56% of homes nearby

Lot size0.21 ac
SmallerTypical 0.22 acBigger

Bigger than 41% of homes nearby

Year built1941
OlderTypical 1965Newer

Newer than 3% of homes nearby

How 21 S William St ranks against every home in each area.
MeasureThis homeMount Prospect 60056Cook County
Estimated valuepricier than$440,32252% of homes70% of homes
Price per ft²pricier than$27943% of homes62% of homes
Living areabigger than1,581 ft²56% of homes56% of homes
Lot sizebigger than0.21 ac41% of homes65% of homes
Year builtnewer than19413% of homes30% of homes

About 21 S William St

How much is 21 S William St, Mount Prospect, IL worth?

The TopHap Estimate for 21 S William St, Mount Prospect, IL is $440,322 as of Aug 30, 2026. The likely range is $405,336 to $475,308. The estimate is modelled from recorded sales, assessments and the property's own characteristics — it is not an appraisal.

When did 21 S William St, Mount Prospect, IL last sell?

21 S William St, Mount Prospect, IL last sold on Feb 28, 1994 for $189,000, according to the county's recorded deed.

How big is 21 S William St, Mount Prospect, IL?

21 S William St, Mount Prospect, IL has 4 bedrooms, 2 bathrooms, 1,581 square feet of living space and a 0.21-acre lot.

When was 21 S William St, Mount Prospect, IL built?

21 S William St, Mount Prospect, IL was built in 1941, making it 85 years old. It is a old style home. The building has 2 stories.

What schools serve 21 S William St, Mount Prospect, IL?

21 S William St, Mount Prospect, IL is assigned to Lincoln Middle School (middle), rated B+; Prospect High School (high), rated A+; Westbrook Early Learning Center (elementary). All sit in Mount Prospect School District 57. Attendance boundaries change — confirm with the district before relying on an assignment.

How does 21 S William St, Mount Prospect, IL compare to other homes in Mount Prospect 60056?

Among the 17,955 homes in Mount Prospect 60056, it is worth more than 52% of them ($440,322 against a typical $437,185), its price per square foot is higher than 43% of them ($279 against a typical $289), it is bigger than 56% of them (1,581 ft² against a typical 1,475 ft²), its lot is bigger than 41% of them (0.21 ac against a typical 0.22 ac) and it is newer than 3% of them (1941 against a typical 1965). Measured against all of Cook County, it is worth more than 70% 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 S William St, Mount Prospect, IL?

The 2023 property tax bill for 21 S William St, Mount Prospect, IL was $9,104. The county assessed it at $36,000.

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