Postal Primer: ZIP Codes and Boundary Review Process

The United States Postal Service (USPS) establishes postal ZIP codes to assist in the efficient sorting and routing of mail. As of March 5, 2022, there were 41,683 ZIP codes in the United States.

This In Focus provides a brief history of postal ZIP codes and information on the processes to establish a new ZIP code or change existing ZIP code boundaries.

Postal and Nonpostal Use of ZIP Codes

USPS developed postal ZIP codes to facilitate automated sorting of mail. However, researchers and data analysts 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. Between 1943 and 1963, mail volume doubled. To handle the increased volume, the Post Office Department introduced the Zoning Improvement Plan (ZIP) to improve the efficiency of mail sorting and delivery.

In July 1963, the Post Office Department introduced nationwide five-digit ZIP codes and began a marketing and education campaign using a cartoon letter carrier, Mr. ZIP.

Figure 1. Mr. ZIP

Source: USPS, "Postal History," https://about.usps.com/who/profile/history/pdf/mr-zip.pdf.

The goal of the campaign was to familiarize the public with the new postal ZIP codes and encourage customers to use ZIP codes consistently when addressing their mail.

In 1983, USPS introduced ZIP+4 codes, which allow mail to be further sorted by block, street, or building.

Components of a Postal ZIP Code

According to USPS, the first number of a ZIP code represents a broad geographic area (see Figure 2). For example, ZIP codes for addresses in the Northeast begin with "0" and ZIP codes on the West coast begin with "9." The next two numbers represent regional areas, while the last two represent specific post offices or postal zones. Generally, the first three numbers of a ZIP code correspond to the USPS Sectional Center Facility that processes and distributes mail for the geographic area.

Figure 2. USPS ZIP Code Map

Source: USPS, "Postal Facts."

Customers may look up ZIP codes by address (or cities by ZIP code) using the USPS ZIP Code lookup tool at https://tools.usps.com/zip-code-lookup.htm.

ZIP Code Boundary Review Process

USPS may establish a new ZIP code based on an internal review of ZIP code assignments. Alternatively, USPS may establish a new ZIP code following a ZIP code boundary 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 routes and may not correspond to municipal or perceived community boundaries.

Submission of Documentation

The ZIP Code Boundary Review Process requires any municipality or community group seeking a ZIP code change to submit the request in writing to the USPS district manager who is responsible for the area along with any rationale and justification. Alternatively, requests may be submitted to a local postmaster, who will forward the request and accompanying documentation to the district manager.

The local postmaster is not the decisionmaker in this process. Instead, the district manager is to identify all relevant issues and potential solutions to them, quantify the specific operational impacts and feasibility of the request, meet with the group of proponents to discuss issues and explain potential alternatives, and provide a final determination within 60 days of receiving the request.

Factors Considered

When considering a request for a new ZIP code, USPS considers factors that may affect its capacity to efficiently deliver mail, such as estimated growth in the number of delivery points. USPS encourages proponent groups to provide documentation of anticipated business and retail developments that may require new delivery points or increase mail volume in the area.

The 2016 Management Instruction suggests that community requests to change existing ZIP code boundaries be consistent with formally established municipal boundaries. USPS suggests that proponents provide documented endorsement of the request from local government officials.

After a municipality or community group has submitted a request to USPS, the district manager will identify internal and external issues, including

• whether the requested boundary is "cohesive and manageable" for mail delivery,
• if the revised or new boundary would create duplicate street addresses within a single ZIP code,
• if existing facilities can accommodate the change, and
• how the change might impact timeliness of mail delivery and customer satisfaction.

The district manager will estimate the workhours and costs associated with the proposal, including changes in daily mileage for mail carriers, new facilities or equipment that may be required, costs to reprogram automated mail sorting equipment, and costs of handling misdirected mail.

Generally, USPS limits its consideration to factors that involve mail delivery. However, USPS will reasonably consider factors related to community identity, particularly if the request is from an undeveloped or newly developed area.

Survey of Affected Customers

If USPS considers granting the request, the local postmaster will arrange a meeting with the proponent group to discuss USPS's proposed accommodation. If an agreement is reached with the group, USPS will commission a formal survey of customers who would be affected by the proposed change. The survey informs customers of the nature and scope of the proposed change (e.g., town name and/or ZIP code) and the implementation date. A simple majority of the survey respondents is adequate for approval.

Determination

When a request is approved, USPS will notify affected customers by mail. Generally, USPS provides customers with a one-year transition period during which they may use the old or the new ZIP code. Customers who continue to use their old ZIP code after one year may experience delivery delays due to misdirected mail.

The district manager must notify the proponent group in writing if its ZIP code request was denied. The notification must include specific justifications for the denial, must be based on the results of the analysis, and must advise the proponent group of the appeal process.

ZIP Code Boundary Appeal Process

The proponent group may appeal to headquarters if the ZIP code request is denied. Any appeals must be submitted within 45 days of the district manager's final decision. Adverse decisions may be appealed, except in cases where a ZIP code request was denied because of the results of the customer survey. The USPS Manager, Rural Delivery, handles all appeals, including those from urban and suburban areas. Appeals should be submitted to:

Manager, Rural Delivery
U.S. Postal Service
475 L'Enfant Plaza, SW, Room 7416
Washington, DC 20260-7340

Alternative Accommodations

A compromise solution that does not involve changing USPS's existing delivery structure is to allow customers to use an alternative city name while keeping the same ZIP code. This situation most commonly occurs when multiple communities fall within the boundaries of a single ZIP code. According to USPS, alternative administrative solutions such as this should be pursued "to the extent reasonably practicable." USPS further states that a ZIP code boundary change should be considered only in cases where there is no reasonable administrative option.

Designating a ZIP Code by Statute

Congress may introduce legislation that, if enacted, would require USPS to create a single ZIP code for a specified community. The most recent example of a ZIP code created by statute occurred in 2006 as part of the Postal Accountability and Enhancement Act (P.L. 109-435). Section 1009 of the act required the creation of unique ZIP codes for (1) Auburn Township, OH; (2) Hanahan, SC; (3) Bradbury, CA; and (4) Discovery Bay, CA.