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June 14, 2022
Postal Primer: ZIP Codes and Boundary Review Process
The United States Postal Service (USPS) establishes postal
Components of a Postal ZIP Code
ZIP codes to assist in the efficient sorting and routing of
According to USPS, the first number of a ZIP code
mail. As of March 5, 2022, there were 41,683 ZIP codes in
represents a broad geographic area (see Figure 2). For
the United States.
example, ZIP codes for addresses in the Northeast begin
with “0” and ZIP codes on the West coast begin with “9.”
This In Focus provides a brief history of postal ZIP codes
The next two numbers represent regional areas, while the
and information on the processes to establish a new ZIP
last two represent specific post offices or postal zones.
code or change existing ZIP code boundaries.
Generally, the first three numbers of a ZIP code correspond
to the USPS Sectional Center Facility that processes and
Postal and Nonpostal Use of ZIP Codes
distributes mail for the geographic area.
USPS developed postal ZIP codes to facilitate automated
sorting of mail. However, researchers and data analysts
Figure 2. USPS ZIP Code Map
frequently turn to ZIP codes as a tool for organizing and
presenting data. For example, public opinion pollsters often
ask respondents for their ZIP codes so that survey data may
be weighted by geographic region. Auto insurance
premiums are typically based, in part, on traffic and crime
statistics within a customer’s ZIP code. Postal ZIP codes do
not always align with recognized municipal boundaries.
This is because ZIP code boundaries are based on mail
routes and delivery points rather than geographic factors.
History of Postal ZIP Codes
The U.S. Post Office Department, predecessor to USPS,
developed a zoning address system in 1943 as a way to
make sorting and delivery of mail easier. The first postal
zones were one to two digits and used in large cities only.
Source: USPS, “Postal Facts.”
Between 1943 and 1963, mail volume doubled. To handle
the increased volume, the Post Office Department
Customers may look up ZIP codes by address (or cities by
introduced the Zoning Improvement Plan (ZIP) to improve
ZIP code) using the USPS ZIP Code lookup tool at
the efficiency of mail sorting and delivery.
https://tools.usps.com/zip-code-lookup.htm.
ZIP Code Boundary Review Process
In July 1963, the Post Office Department introduced
nationwide five-digit ZIP codes and began a marketing and
USPS may establish a new ZIP code based on an internal
review of ZIP code assignments. Alternatively, USPS may
education campaign using a cartoon letter carrier, Mr. ZIP.
establish a new ZIP code following a ZIP code boundary
Figure 1. Mr. ZIP
review that was initiated by a request from the public.
Requests to change existing ZIP code boundaries are
subject to the same process.
The 2016 USPS “Management Instruction: ZIP Code
Boundary Review Process” outlines USPS’s policies to
consider and, if possible, accommodate requests to modify
ZIP code boundaries or change the last lines of an address
(e.g., the city or town name). According to USPS, ZIP code
assignments depend largely on delivery areas and postal
Source: USPS, “Postal History,” https://about.usps.com/who/profile/
routes and may not correspond to municipal or perceived
history/pdf/mr-zip.pdf.
community boundaries.
The goal of the campaign was to familiarize the public with
the new postal ZIP codes and encourage customers to use
Submission of Documentation
ZIP codes consistently when addressing their mail.
The ZIP Code Boundary Review Process requires any
municipality or community group seeking a ZIP code
In 1983, USPS introduced ZIP+4 codes, which allow mail
change to submit the request in writing to the USPS district
to be further sorted by block, street, or building.
manager who is responsible for the area along with any
rationale and justification. Alternatively, requests may be
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Postal Primer: ZIP Codes and Boundary Review Process
submitted to a local postmaster, who will forward the
scope of the proposed change (e.g., town name and/or ZIP
request and accompanying documentation to the district
code) and the implementation date. A simple majority of
manager.
the survey respondents is adequate for approval.
The local postmaster is not the decisionmaker in this
Determination
process. Instead, the district manager is to identify all
When a request is approved, USPS will notify affected
relevant issues and potential solutions to them, quantify the
customers by mail. Generally, USPS provides customers
specific operational impacts and feasibility of the request,
with a one-year transition period during which they may
meet with the group of proponents to discuss issues and
use the old or the new ZIP code. Customers who continue
explain potential alternatives, and provide a final
to use their old ZIP code after one year may experience
determination within 60 days of receiving the request.
delivery delays due to misdirected mail.
Factors Considered
The district manager must notify the proponent group in
When considering a request for a new ZIP code, USPS
writing if its ZIP code request was denied. The notification
considers factors that may affect its capacity to efficiently
must include specific justifications for the denial, must be
deliver mail, such as estimated growth in the number of
based on the results of the analysis, and must advise the
delivery points. USPS encourages proponent groups to
proponent group of the appeal process.
provide documentation of anticipated business and retail
developments that may require new delivery points or
ZIP Code Boundary Appeal Process
increase mail volume in the area.
The proponent group may appeal to headquarters if the ZIP
code request is denied. Any appeals must be submitted
The 2016 Management Instruction suggests that community
within 45 days of the district manager’s final decision.
requests to change existing ZIP code boundaries be
Adverse decisions may be appealed, except in cases where
consistent with formally established municipal boundaries.
a ZIP code request was denied because of the results of the
USPS suggests that proponents provide documented
customer survey. The USPS Manager, Rural Delivery,
endorsement of the request from local government officials.
handles all appeals, including those from urban and
suburban areas. Appeals should be submitted to:
After a municipality or community group has submitted a
request to USPS, the district manager will identify internal
Manager, Rural Delivery
and external issues, including:
U.S. Postal Service
475 L’Enfant Plaza, SW, Room 7416
whether the requested boundary is “cohesive and
Washington, DC 20260-7340
manageable” for mail delivery,
Alternative Accommodations
if the revised or new boundary would create duplicate
A compromise solution that does not involve changing
street addresses within a single ZIP code,
USPS’s existing delivery structure is to allow customers to
use an alternative city name while keeping the same ZIP
if existing facilities can accommodate the change, and
code. This situation most commonly occurs when multiple
communities fall within the boundaries of a single ZIP
how the change might impact timeliness of mail
code. According to USPS, alternative administrative
delivery and customer satisfaction.
solutions such as this should be pursued “to the extent
reasonably practicable.” USPS further states that a ZIP code
The district manager will estimate the workhours and costs
boundary change should be considered only in cases where
associated with the proposal, including changes in daily
there is no reasonable administrative option.
mileage for mail carriers, new facilities or equipment that
may be required, costs to reprogram automated mail sorting
Designating a ZIP Code by Statute
equipment, and costs of handling misdirected mail.
Congress may introduce legislation that, if enacted, would
require USPS to create a single ZIP code for a specified
Generally, USPS limits its consideration to factors that
community. The most recent example of a ZIP code created
involve mail delivery. However, USPS will reasonably
by statute occurred in 2006 as part of the Postal
consider factors related to community identity, particularly
Accountability and Enhancement Act (P.L. 109-435).
if the request is from an undeveloped or newly developed
Section 1009 of the act required the creation of unique ZIP
area.
codes for (1) Auburn Township, OH; (2) Hanahan, SC; (3)
Bradbury, CA; and (4) Discovery Bay, CA.
Survey of Affected Customers
If USPS considers granting the request, the local postmaster
Michelle D. Christensen, Analyst in Government
will arrange a meeting with the proponent group to discuss
Organization and Management
USPS’s proposed accommodation. If an agreement is
reached with the group, USPS will commission a formal
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survey of customers who would be affected by the proposed
change. The survey informs customers of the nature and
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Postal Primer: ZIP Codes and Boundary Review Process
Disclaimer
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