What Is 00501

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Last updated: April 11, 2026

Quick Answer: 00501 is the lowest ZIP code number in the United States, assigned exclusively to the Internal Revenue Service (IRS) facility in Holtsville, New York. The IRS Brookhaven Campus at this location, established in 1972, handles tax processing and taxpayer correspondence for the northeastern region and processes high volumes of mail.

Key Facts

00501 is the lowest ZIP code number in use in the continental United States
The IRS facility was opened in Holtsville on a 67-acre site in 1972
It is a single-entity ZIP code assigned exclusively to the IRS Brookhaven Campus, not a residential area
The facility is located at 1040 Waverly Avenue in Suffolk County, New York
00501 handles tax processing and taxpayer correspondence for the entire northeastern region of the United States

Overview

00501 is the lowest ZIP code number in the United States, a unique designation that belongs exclusively to the Internal Revenue Service (IRS) facility located in Holtsville, New York. Unlike traditional ZIP codes that serve residential neighborhoods or towns, 00501 is a single-entity ZIP code created specifically for an organization that receives massive volumes of mail annually.

The IRS Brookhaven Campus operates from this special ZIP code, handling a significant portion of the nation's tax processing and taxpayer correspondence. Established in 1972 on a 67-acre site in Suffolk County, the facility has become integral to the IRS's operations in the northeastern United States. The choice of this particular number reflects the postal system's organizational logic, where lower ZIP codes were historically assigned to the northeastern region of the country.

How It Works

Single-entity ZIP codes like 00501 function differently from standard residential or commercial ZIP codes. Here's how 00501 operates within the broader postal system:

Exclusive Assignment: The ZIP code 00501 is assigned exclusively to the IRS Brookhaven Campus and cannot be used for any other purpose or organization. This ensures that all mail directed to this facility receives proper routing and processing.
High-Volume Mail Processing: The facility was designated this special ZIP code because it processes an extraordinarily large volume of incoming and outgoing mail related to tax returns, correspondence, and documents from across the northeastern region.
Regional Tax Processing: The Brookhaven Campus serves as a major processing center for the IRS, handling tax documents and correspondence for multiple states in the northeastern United States, making efficient mail routing critical to operations.
Postal Service Priority: Single-entity ZIP codes like 00501 receive special handling from the United States Postal Service to ensure timely delivery and processing of the massive daily mail volume arriving at the facility.
Standardized Routing: All taxpayer correspondence and documents addressed to the IRS in the Northeast can be routed through ZIP code 00501, streamlining the sorting and delivery process across the postal network.

Key Comparisons

Understanding how 00501 differs from other ZIP codes helps clarify its unique status in the American postal system:

Characteristic	Standard ZIP Code	Single-Entity ZIP Code (00501)
Geographic Coverage	Serves multiple residential or commercial addresses within a defined area	Assigned exclusively to a single organization (IRS facility)
Population/Usage	Typically serves hundreds to thousands of residents or businesses	Serves only the IRS Brookhaven Campus facility with no residential component
Mail Volume	Variable depending on residential density and commercial activity	Handles extremely high volume (millions of pieces annually) requiring special postal handling
Assignment Purpose	Geographic organization based on location and population density	Functional organization based on mail volume and processing needs of a major institution
Assignment Frequency	Assigned based on Census data and demographic changes	Assigned based on organizational need and USPS capacity requirements

Why It Matters

The existence and designation of ZIP code 00501 hold significance for several reasons within the context of American infrastructure and tax administration:

Efficient Tax Processing: By assigning a dedicated ZIP code to the IRS Brookhaven Campus, the postal system ensures that millions of tax returns, payments, and correspondence are routed efficiently without overwhelming standard geographic ZIP codes.
Historical Significance: As the lowest-numbered ZIP code in the United States, 00501 represents the postal system's organizational hierarchy, with lower numbers historically assigned to the northeast. This makes it a notable fixture in American postal history and geography.
Operational Necessity: The IRS facility processes tax documents from across the entire northeastern region, making a dedicated ZIP code essential for managing the enormous daily mail volume while maintaining accuracy and timeliness in document routing.
Postal System Innovation: Single-entity ZIP codes like 00501 demonstrate how the postal system adapts to serve large institutions and government operations that don't fit traditional geographic ZIP code frameworks.

ZIP code 00501 represents a practical solution to a significant logistical challenge: how to efficiently process and route millions of pieces of mail annually for a critical government institution. Its status as the lowest ZIP code in the nation also makes it a point of interest for postal history enthusiasts and those curious about American infrastructure. The Holtsville facility continues to play a vital role in the nation's tax administration, and its unique ZIP code ensures that tax-related correspondence reaches the correct destination swiftly and reliably, supporting the broader functioning of the American tax system.