Retail window hours
When a person is behind the counter to sell stamps, weigh a parcel, or hand over a package held for pickup. This is usually shorter than the lobby stays open.
Finding the branch
A PO Box lives at the Post Office its ZIP code names
A PO Box has no street address of its own. The ZIP printed after it belongs to a real building — a Post Office with a lobby, a retail counter and its own hours — and that building is where the box physically sits. Two USPS tools turn that bare ZIP into a street address: the Post Office Locator, which returns the branch itself, and the ZIP Code Lookup, which reads back the city behind any ZIP when you only have that much. Both were read live at tools.usps.com on 2026-08-30.
USPS Locator, datedZIP Code Lookup, datedWhat neither one discloses
The ZIP is the address
A box number tells you nothing on its own. The five digits after it tell you which building to look up.
Two lookups, and which one to start with
Which tool goes first depends on what you already have. USPS describes the Locator's job plainly: it lets a visitor "search for nearby Post Office locations, Collection Boxes, Self-Service Kiosks, and services like PO Boxes and Money Orders" by street address, city and state, ZIP code, or current location. Feed it the ZIP straight off the box address and, filtered to Post Offices, it names the one branch that ZIP belongs to.
| What you have | Start with | What comes back |
|---|---|---|
| A trusted 5-digit ZIP off the box address | Post Office Locator, searched by that ZIP | The specific branch: street address, phone, hours |
| Only a city and state, no ZIP you trust | Post Office Locator, searched by city and state | Every Post Office in that city, PO Box service flagged |
| A bare ZIP with no city attached | ZIP Code Lookup's Cities by ZIP Code function | The city and state that ZIP serves, to feed into the Locator next |
The Cities by ZIP Code function exists for exactly this direction of lookup — USPS's own description of it is reverse: type in a ZIP code to "see the cities it covers." That is a smaller, faster step than the full Locator when a ZIP is all you were handed and you just need a city name before deciding whether the shipment is even domestic.
What a matched result actually contains
A Locator result for a Post Office is a profile of the building, not a directory of who uses it. For each match, USPS returns the street address and a contact phone number, regular retail window hours, after-hours lobby access where the building has it, and whether PO Box service and box-access hours are offered at that location, alongside the services the counter handles — passport appointments, hold mail, package pickup.
Lobby and box access hours
Many branches let boxholders into the lobby well outside window hours to check and empty a box with their own key, even when nobody is staffing the counter.
Distance and map
Results can be filtered by a radius of 1 to 100 miles and sorted by distance, which matters when the ZIP on a box turns out to serve a facility a few towns over from the name on the address.
When the label already names the building
Some PO Box addresses skip the lookup step entirely. When a label reads a real street number and name, followed by a box number preceded by # or UNIT, that street address already is the Post Office — USPS calls this option Street Addressing, and it is covered in full, along with how to spot it, in our guide to telling a PO Box from a real address. There is nothing left to locate in that case: the building name is already printed on the label, and only the box number after it tells you it is not a suite in an office park.
What neither tool will hand you
A boxholder's name is not part of either result. The Locator profiles the facility — address, hours, phone, which services the counter offers — and the ZIP Code Lookup only resolves geography; neither one exposes who is renting inside the building. That is by design rather than an omission: a member of the public gets the building a box sits in, never its tenant, and USPS keeps that distinction the same way any landlord would keep a resident directory off the mailbox itself.
A seller trying to chase down a buyer behind a PO Box, or a buyer trying to confirm a seller is a real business before paying, will not settle that question with these tools. That is a trust problem, not an address problem, and it sits outside what a locator can answer.
Why the branch matters more to a shipper than the city does
The most common reason to run this lookup is not curiosity about geography. It is a seller staring at a customer's PO Box, wondering which carrier to buy. That question has one answer regardless of which city the box sits in: FedEx and UPS are not authorized to deliver to a bare USPS PO Box number, in any branch, in any state, so the carrier decision is made before the location lookup ever starts. Confirming the branch is still worth doing — it tells you the ZIP is a real, staffed USPS destination rather than a typo — but it will not turn a PO Box into a FedEx-reachable address. Our page on FedEx and PO Boxes and the matching one for UPS cover that limit directly, and what a PO Box costs and what can reach it lays out the deliverability gap across carriers on one lane.
Where these rules come from
- USPS, Post Office Locator — search methods and what a matched location returns. Read 2026-08-30.
- USPS, ZIP Code Lookup, Cities by ZIP Code — resolving a ZIP to the city and state it serves. Read 2026-08-30.
- USPS, PO Boxes — the product page pointing to Find USPS Locations for PO Box search. Read 2026-08-30.
USPS updates branch hours and service availability without notice. Treat a Locator result as current on the day you pulled it, and re-check before relying on lobby or window hours for anything time-sensitive.
PO Box location questions
Where is a PO Box physically located?
Inside the Post Office named by its own ZIP code. A PO Box is a locked compartment in that building's lobby, not a separate street address, so locating the box means locating the branch behind the ZIP.
How do I find the Post Office behind a specific PO Box?
Search the box's ZIP code in the USPS Post Office Locator at tools.usps.com. If you are not sure the ZIP is right, run it through the ZIP Code Lookup's Cities by ZIP Code function first to confirm the city, then feed that into the Locator.
What does the Locator actually tell me about that branch?
Its street address and phone number, regular retail window hours, after-hours lobby access, and whether PO Box service and access hours are offered there — everything the Locator holds is about the building, not about who rents inside it.
Can I find out who rents a specific PO Box?
Not through either tool. Both return facility information only — an address, hours, a phone number — and neither one exposes a customer name. USPS treats boxholder identity as its own record, not a public lookup.
I only have a buyer's PO Box — does the city it sits in matter?
Less than the fact that it is a PO Box at all. FedEx and UPS cannot deliver to a bare box number in any city, so the branch location mostly confirms the ZIP is a real, working USPS destination before you buy a label on it.