Mercer Island ZIP Coverage
Official sources identify one ZIP for standard Mercer Island residential and business delivery. The USPS location record and King County ZIP map agree on the main code, while USPS remains the authority for the exact ZIP+4 assigned to a street address. No second residential code, PO-box-only code, or unique institutional code for the city was found.
| ZIP | Area served | Postal station | Local note |
|---|---|---|---|
| 98040 | Mercer Island city and the island's standard residential and business delivery geography | Mercer Island Post Office, 3040 78th Ave SE | USPS exact-address lookup controls the ZIP+4 and delivery assignment |
The Mercer Island Post Office listing gives its delivery address as Mercer Island, WA 98040-9998 and lists 206-232-8834. That station code does not mean each person with a 98040 mailing address uses the counter. The ZIP code directory records a delivery area, not a roll of patrons or residents.
Verify a Mercer Island ZIP Code
The USPS ZIP Code Lookup is the first stop for one address. It standardizes the delivery line and returns the assigned code. The consumer form does not establish parcel ownership, city jurisdiction, precinct, or occupancy. Those questions belong to other custodians.
| USPS field | Input and purpose |
|---|---|
| Street address | Full delivery address used for an address-specific match |
| City | Enter Mercer Island as the postal city for the current address |
| State | Select Washington |
| Result | Standardized address with ZIP or ZIP+4 when available |
Keep the standardized line with the search date. If an old letter uses East Seattle, Seattle, King County, or a rural route, preserve that form too. Historical records may remain indexed under the earlier place name even when USPS now returns Mercer Island.
Find Mercer Island Residents by ZIP
Most official local tools do not offer a ZIP-wide resident search. A careful workflow uses 98040 to narrow geography, then changes to the field each custodian actually indexes. This avoids the false promise that one code produces a current household list.
- Confirm the full street address through USPS and save its standardized postal form.
- Open King County Parcel Viewer and search the address, parcel number, or map point.
- Use the parcel report to retain the ten-digit parcel ID, legal description, and jurisdiction.
- Check a known person's voter registration with the required matching fields, not the ZIP alone.
- Use a genuine ZIP field, such as Washington unclaimed property, only when that record type fits the search.
Once the search has narrowed to an address or road, the Mercer Island street directory handles the parcel-by-parcel path. It is a different task from ZIP geography and gives the address-level record chain.
Mercer Island Portals Without ZIP Filters
King County eReal Property currently starts with a property tax account or parcel number. Parcel Viewer accepts an address, parcel number, or map click. Neither public landing page documents a ZIP filter or promises a ZIP-wide export. The Mercer Island Map Portal likewise searches an address or parcel ID for permit and land-use documents.
King County My Voter Information has no ZIP field. It asks for any three of first name, last name, date of birth, and house or building number. Public-file requests may be scoped by political jurisdiction or precinct, but the research did not locate a current fee or exact ZIP-filter option. Do not turn that absence into an assumed feature.
Note: Use the county ZIP map for area context, then search individual parcels or known names in the proper official portal.
A Real Mercer Island ZIP Search
The Washington Department of Revenue unclaimed-property search is one official tool that expressly accepts ZIP Code. It can pair the code with a last or business name, first name, city, or property ID. A hit means the state holds property under that indexed identity. It does not prove a present address.
| Search field | What it does |
|---|---|
| Last or business name | Primary person or entity text field |
| First name | Narrows a personal-name search |
| City | Add Mercer Island as a location clue |
| ZIP | Use 98040 to narrow the indexed address geography |
| Property ID | Returns to a known state record identifier |
Claim documentation is required before funds or property are released. Treat the search result as a lead tied to the agency's record, and use the claim ID or property ID for any follow-up.
Mercer Island ZIP and City Lines
ZIP Codes are delivery constructs made by USPS. City limits are legal municipal boundaries. King County's official ZIP boundary map overlays postal polygons with incorporated areas and labels 98040 over Mercer Island. That visual overlap is strong, but the two kinds of boundary are not legally identical at every edge.
A school zone, voting precinct, parcel, and ZIP can all divide the same landscape in different ways. USPS answers where mail goes. King County Parcel Viewer answers which parcel and reports apply. Elections identifies a registration and precinct. Mercer Island GIS links the parcel to permits and land-use files. Keep each result in its lane.
- ZIP Code
- A USPS delivery-area code, not a city boundary or list of occupants.
- ZIP+4
- The basic five digits plus four more digits that refine a delivery segment.
- PO-box ZIP
- A code reserved for post-office boxes; no separate one was located for Mercer Island.
- Unique ZIP
- A code assigned to one large recipient; no Mercer Island example was located.
- Carrier route
- A postal delivery sequence that is more detailed than the five-digit area.
98040 and Mercer Island History
Modern postal data can hide the place names used in an older index. Before incorporation, island property was under King County. The City of Mercer Island and a Town of Mercer Island centered mainly on Town Center incorporated separately in 1960, then merged on May 19, 1970. City material warns that many Town records were not retained.
The official city pages conflict on whether the city incorporation date was July 5 or July 18, 1960. Keep both dates flagged until the City Clerk resolves the difference. The Town's August 9, 1960 incorporation and the 1970 merger are stated separately. For a historical search, try the modern Mercer Island and 98040 terms alongside Town of Mercer Island, Seattle, East Seattle, King County, and rural-route forms.
A parcel number, plat, lot and block, or legal description provides the stable bridge when postal labels change. King County uses ten-digit parcel IDs in its assessor and recorder workflows. The legal land identity should control a long address history, while the ZIP code directory controls only the postal slice.
One Mercer Island Residential ZIP
The research found no official Mercer Island ZIP split or realignment notice. A 2015 state planning document uses 98040 for the city, while the inspected King County map dates to 2013. Those sources support the current broad pattern, but they do not replace today's address-specific USPS check.
Likewise, no separate residential, PO-box-only, or institutional ZIP was located. That negative finding should remain precise. It does not prove that every edge case, internal delivery rule, or future assignment is fixed. Verify the full address whenever the exact code matters.
Cite a Mercer Island ZIP Match
A strong address citation keeps four distinct identifiers when they are available: the USPS-standardized address, the King County parcel number, the legal description, and the political jurisdiction or precinct. That set makes clear which agency confirmed each part of the place.
A ZIP result alone is not a resident match. An assessor's owner name is not proof of an occupant, and a tax mailing address may differ from the island situs address. A voter result confirms a registration record under statutory limits. A city permit confirms a parcel-linked project or filing. Use the smallest amount of personal data needed and never use public records to stalk, harass, or harm anyone.
Note: Preserve the source URL, record date, and agency identifier so a later reader can repeat the same geographic check.