The search term 00001 ZIP code frequently arises because users assume it must be the first or lowest postal code in the United States.
The direct answer is that 00001 is not a valid, deliverable ZIP Code assigned by the U.S. Postal Service (USPS).
While the ZIP Code system begins its numeric range with zeros (representing the New England region), the lowest official ZIP Code currently in active use is 00501, which is assigned exclusively to the Internal Revenue Service (IRS) Center in Holtsville, New York. This article breaks down the structure of US ZIP Codes, explains why 00001 is not used, and identifies the lowest actual codes.
Why the 00001 ZIP Code is Unassigned
The United States Postal Service (USPS) does not use the 00001 code for general delivery. This is part of the way the postal service structures its geography:
The ZIP Code Structure
The USPS ZIP Code system is based on a geographic hierarchy, where the first digit identifies a large section of the country:
- 0 (Zero): Designates the far eastern states of the US, including New England (Connecticut, Massachusetts, Maine, New Hampshire, New Jersey, Rhode Island, and Vermont) as well as Puerto Rico and the U.S. Virgin Islands.
- 000xx Codes: The lowest codes (000xx) were generally reserved for unique uses, military bases (APO/FPO), or U.S. territories. While codes like 00001 are technically within the postal range, they have never been issued for standard use.
The Actual Lowest ZIP Code
The lowest ZIP Code in regular use and the one most commonly mistaken for 00001 is 00501.
| ZIP Code | Location / Usage | Type |
| 00001 | Invalid / Unassigned | None |
| 00501 | Holtsville, New York (Exclusively for the IRS Center) | Unique ZIP |
| 01001 | Agawam, Massachusetts | Lowest code for a general city/town |
Geographic Assignment of Codes Beginning with ‘0’
When entering a ZIP Code online, any code starting with a zero confirms the address is in the northeastern region of the United States.
| First 3 Digits (Prefix) | State(s) Covered | Primary Hub |
| 005xx | New York (Unique to IRS) | Holtsville, NY |
| 006xx – 009xx | Puerto Rico / U.S. Virgin Islands | San Juan, PR |
| 010xx – 027xx | Massachusetts, Rhode Island | Springfield, MA |
| 030xx – 049xx | New Hampshire, Vermont, Maine | Portland, ME |
| 070xx – 089xx | New Jersey | Newark, NJ |
Note: If an online form requires a valid ZIP Code and 00001 is not accepted, the system is likely validating against the official USPS database, which does not contain the 00001 entry.
Frequently Asked Questions (FAQ)
What is the highest U.S. ZIP Code?
The highest currently used ZIP Code in the United States is 99950, which corresponds to Ketchikan, Alaska. The highest digit (9) designates the far western region of the country.
Why do some people use 00001 for online forms?
People sometimes use 00001 or other non-existent codes (like 90210, 10001, or 12345) as filler when a website mandates a ZIP Code but the user doesn’t want to provide their real location, or if the form only requires the format of a 5-digit number and doesn’t validate against the USPS database. However, using 00001 may lead to validation errors.
How do I look up the correct ZIP Code for an address?
The most reliable way to find a correct ZIP Code is to use the official USPS ZIP Code Lookup tool on the United States Postal Service website. You can look up the code by entering the street address and city/state.
Conclusion
While the number 00001 seems logical as the first postal identifier, it is not a valid or assigned ZIP Code in the U.S. postal system. The official lowest ZIP Code in use is 00501 (for the IRS Center in Holtsville, NY). When filling out forms, use your actual, official 5-digit ZIP Code or select a valid code such as 01001 if you are asked to provide a low-range New England code.
