County outline
Where Island County is located
Area breakdown
Land accounts for 40.3% of Island County’s measured area and water for 59.7%. Its combined area converts to 1,339.9 square kilometers or approximately 331,087 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 208.698 | 540.525 | 133,566.7 |
| Water | 308.626 | 799.338 | 197,520.6 |
| Total | 517.324 | 1,339.863 | 331,087.4 |
How Island County compares
By original Census land area, Island County ranks #38 of 39 in Washington and #2987 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.12 times the Washington county-equivalent median of 1,738.8 square miles. It accounts for 0.3% of the combined county land area in the state.
See the complete Washington ranking · What counts as a county equivalent?
Population and density of Island County
The Census Bureau estimates that 85,657 people lived in Island County on July 1, 2025. That ranks #697 of 3,222 county equivalents nationally and #16 of 39 in Washington. Since the April 1, 2020 estimates base of 86,856, the population has declined by 1,199 (−1.4%), compared with +3.8% for Washington as a whole.
With 208.7 square miles of land, that is 410 people per square mile (158 per km²), placing Island County #402 nationally for density and #7 in Washington. The median county equivalent has 47 people per square mile; the Washington median is 39. Put another way, there are about 1.6 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 87,001 | 87,606 | 86,738 | 86,194 | 85,982 | 85,657 |
| Change | — | +605 | −868 | −544 | −212 | −325 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in Island County
3 incorporated places lie at least partly in Island County. Together they are home to 27,132 people (31.7%); the other 58,525 (68.3%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Oak Harbor city, with 24,083 residents in the county. The county seat, Coupeville town, has 1,920 residents.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Oak Harbor city | 24,083 | −2.2% | 9.675 |
| Coupeville townCounty seat | 1,920 | −1% | 1.27 |
| Langley city | 1,129 | −1.8% | 1.008 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Island County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Island County is a central county of the Oak Harbor, WA Micropolitan Statistical Area. Island County is the area’s only county equivalent, so the micro area has the same 208.7 square miles of land. By combined land it ranks #534 of 542 micropolitan areas, and #58 by population. It belongs to the Seattle-Tacoma, WA Combined Statistical Area.
ZIP codes
8 ZIP Code Tabulation Areas have land in Island County, and each lies mostly inside the county.
9823698239982499825398260982779827898282
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering Island County
Island County shares a land border with 1 county equivalent. Snohomish County has 10 times its land area.
| Bordering county equivalent | Land mi² | Size vs. Island | Compare |
|---|---|---|---|
| Snohomish County | 2,086.5 | 10× larger | Compare |
How big is Island County compared with U.S. states?
Island County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 5 times as much. Washington’s county land could hold about 318 areas the size of Island County.
Another way to picture it: the same land area would fill a square about 14.4 miles (23.2 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about Island County?
Island County has more land than 235 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places Island County at #2,111 nationally by total area, 876 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.
Its water share is 59.7%, compared with a national county-equivalent median of 1.2% — 58.5 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside Island County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #2986 | Lee County, Kentucky | 208.8 | Compare |
| #2987 | Island County, Washington | 208.7 | This county |
| #2988 | Franklin County, Kentucky | 207.9 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 48.158554, -122.670649. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 540,526,427 m²; AWATER: 799,338,267 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is Island County?
Island County, Washington has 208.7 square miles (540.5 km²) of land and 308.6 square miles of water, for a total area of 517.3 square miles. It ranks #2987 of 3,222 U.S. county equivalents by land area.
Is Island County the largest county in Washington?
No. Island County ranks #38 of 39 in Washington by land area. The largest is Okanogan County, with 5,266.2 square miles of land.
What counties border Island County?
Island County shares a land border with Snohomish County.
What is the population of Island County?
The Census Bureau estimates Island County had 85,657 residents on July 1, 2025, ranking #697 of 3,222 county equivalents. That is 410 people per square mile of land.
What is the county seat of Island County?
The county seat of Island County is Coupeville.
What cities and towns are in Island County?
Island County has 3 incorporated places. The most populous are Oak Harbor city, Coupeville town, and Langley city; 58,525 residents live outside any incorporated place.
Is Island County part of a metropolitan area?
Yes. It is a central county of the Oak Harbor, WA Micropolitan Statistical Area.
How many ZIP codes are in Island County?
8 ZIP Code Tabulation Areas have land in Island County, and 8 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Island County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 5 times as much land.
How many acres of land are in Island County?
The land measurement converts to approximately 133,567 acres. Including water, total area is approximately 331,087 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.