Mercer Island is a city in King County, Washington, home to about 25,307 people across 6.4 square miles. Its ZIP code is 98040.
Homes sold for a median of $799 per square foot in the three months ending August 2026, a seller’s market.
Each card is that ZIP code’s whole market, including any part outside Mercer Island. Seller’s market: under 4 months of supply; buyer’s market: over 6. Methodology
We’re writing up Mercer Island’s story and what everyday life there is like, for people thinking about moving in.
Are you a local agent who knows Mercer Island well? Agents who advertise here will be able to write the guide. Advertise on OfferBacked
| Nearest major airport | Seattle–Tacoma International Airport (SEA)9 miles away |
|---|---|
| Nearest city of 250,000+ | Seattle, WA7 miles away |
Straight-line distances from the center of Mercer Island; driving is longer.
Source: Airports from OurAirports (scheduled passenger service); city centers and populations from the U.S. Census Bureau.
Source: Members of Congress from the congress-legislators project; districts from the Census Bureau’s relationship files; governor and mayor from Wikidata.
Mercer Island had 25,748 residents in the 2020 census, up 17% since 2000.
It’s the 52nd largest of 628 towns in Washington by population.
King County grew from 110,053 residents in 1900 to 2,269,675 in 2020.
King County, 1900–2020
Source: U.S. Census Bureau decennial censuses (counties 1900–1990 from the Bureau’s historical county file).
Average highs peak around 77°F in summer, and winter lows average 36°F. About 36.5 inches of rain and melted snow fall in a typical year.
Source: NOAA 1991–2020 climate normals, Seattle Boeing Fld, WA weather station (4 miles away).
1,305,947 jobs at 70,376 businesses in King County. The biggest industries by employees:
Source: U.S. Census Bureau County Business Patterns 2023 (private employers; jobs counted where people work).
227 doctors and other health care providers list an office in Mercer Island.
Nearest hospitals
Providers with an office here
| Primary care doctors | 27 |
|---|---|
| Specialist doctors | 29 |
| Dentists | 26 |
| Nurse practitioners and physician assistants | 22 |
| Mental health providers | 62 |
| Physical and occupational therapists | 49 |
| Optometrists | 4 |
| Chiropractors | 8 |
| Pharmacies | 7 |
Source: Hospitals from CMS Hospital General Information (ratings are CMS overall star ratings); straight-line distances; providers from the CMS National Plan and Provider Enumeration System (NPPES), by practice address and primary specialty.
Parks (22 nearby)
Grocery stores (3 nearby)
Pharmacies (2 nearby)
Libraries (1 nearby)
Museums
Theaters and performance venues (2 nearby)
Counts are within about 2 miles of the center of town.
Source: Map data © OpenStreetMap contributors (openstreetmap.org/copyright), as mapped by volunteers; it can miss places or include closed ones.
Public schools here are run by Mercer Island School District. Check each district’s attendance zones for a specific address.
| School | Grades | Students | Type | Distance |
|---|---|---|---|---|
| Northwood Elementary SchoolMercer Island | Pre-K–5 | 398 | Public | 1.0 mi |
| Island Park ElementaryMercer Island | K–5 | 364 | Public | 0.5 mi |
| Lakeridge Elementary SchoolMercer Island | K–5 | 401 | Public | 1.9 mi |
| West Mercer ElementaryMercer Island | K–5 | 431 | Public | 0.8 mi |
| Islander Middle SchoolMercer Island | 6–8 | 960 | Public | 1.6 mi |
| Mercer Island High SchoolMercer Island | 9–12 | 1,439 | Public | 0.9 mi |
| School | Grades | Students | Affiliation | Distance |
|---|---|---|---|---|
| Creative Learning Center LlcMercer Island | Pre-K–K | 4 | Nonsectarian | 2.1 mi |
| Early World MontessoriMercer Island | Pre-K–K | 6 | Nonsectarian | 1.6 mi |
| French American School of Puget SoundMercer Island | Pre-K–8 | 312 | Nonsectarian | 1.5 mi |
| St Monica SchoolMercer Island | Pre-K–12 | 222 | Roman Catholic | 0.7 mi |
| Yellow Wood AcademyMercer Island | 4–12 | 101 | Nonsectarian | 1.4 mi |
| Privett AcademyMercer Island | 7–12 | 74 | Nonsectarian | 1.4 mi |
| Northwest Yeshiva High SchoolMercer Island | 9–12 | 57 | Jewish | 0.4 mi |
Source: U.S. Department of Education, NCES: Common Core of Data (2024-2025) for public schools; Private School Universe Survey (2023-2024) for private schools. Listed by address; we don’t rate schools.
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Town boundaries don’t always match ZIP codes: a ZIP code can cross into neighboring towns, and a town can share a ZIP code with its neighbors. Facts describe the town itself; market figures describe whole ZIP codes.