ZIP Codes in Mercer Island, WA
Mercer Island uses 1 ZIP code, all in King County. Pick one below for details, or look up the full nine-digit ZIP+4 for a specific street address.
All 1 Mercer Island ZIP codes
| ZIP | Type | County | Population |
|---|---|---|---|
| 98040 | standard | King | 25,307 |
Finding a ZIP+4 in Mercer Island
Knowing which of these 1 ZIP codes covers an address only gets you partway. The four-digit extension identifies the specific delivery point — typically one side of one block. Two houses facing each other on the same Mercer Island street almost always have different ZIP+4 codes even though they share all five leading digits.
Appending ZIP+4 to a mailing list?
Upload a CSV of Mercer Island addresses and download it complete.