Once you understand that ZIP codes follow a deliberate east-to-west numbering logic, a natural question follows: which ZIP code is the lowest in the country, and which one is the highest? The answer says a lot about how the entire system was originally laid out, and it's a fun, quick way to see the ZIP code structure in action at its two extremes.
Why Geography Determines the Range
As covered in our breakdown of how ZIP codes are structured, the first digit of a ZIP code represents one of ten broad national zones, arranged roughly from east to west. Zone 0 covers parts of the Northeast, including Puerto Rico and parts of New England, while zone 9 covers the Pacific coast, including Alaska, Hawaii, and US territories in the Pacific. Because of this deliberate geographic ordering, the lowest possible ZIP codes are found in the far Northeast, and the highest are found in the Pacific region.
The Lowest ZIP Codes
The lowest ZIP codes in the country belong to Puerto Rico and parts of the Virgin Islands, both of which fall under the 006 to 009 prefix range as US territories included in the original zone 0 numbering. Within the fifty states themselves, the lowest ZIP codes are found in Massachusetts, Connecticut, and other parts of New England, some starting as low as 010. This isn't a coincidence or a quirk; it directly reflects the original 1963 design decision to start the national numbering sequence in the northeastern United States.
The Highest ZIP Codes
At the opposite end, the highest ZIP codes in the country belong to parts of Alaska and Hawaii, along with some US territories in the Pacific, reaching up toward the 99999 range. Alaska's ZIP codes generally sit in the high 99500s to 99900s range, reflecting its position as one of the furthest points west (and geographically north) in the national numbering system. California, despite being a large and populous Pacific coast state, doesn't actually hold the very highest ZIP codes; that distinction goes to Alaska and the more remote Pacific territories.
Why This Range Isn't Perfectly Symmetrical
It's worth noting that the ZIP code system wasn't designed as a perfectly even east-to-west gradient across exactly ten equal geographic slices. The zone boundaries were drawn based on practical postal routing considerations at the time, existing rail lines, regional distribution hubs, and population centers, rather than a strict, evenly spaced map grid. That's why some states with similar longitudes can still have somewhat different starting ZIP digits, depending on which sectional distribution center historically served that area.
A Few Other Interesting Extremes
Beyond the simple highest and lowest numbers, there are a few other notable extremes worth knowing:
- Largest ZIP code by area tends to belong to sparsely populated regions in Alaska or the rural West, where a single ZIP code can cover thousands of square miles simply because there isn't enough mail volume to justify splitting the area further.
- Smallest ZIP codes by area are typically found in dense urban cores, sometimes covering just a few city blocks, a direct result of high population density requiring finer sorting granularity, a pattern explained in more detail in why does one ZIP code cover multiple cities (the same density logic that splits cities into many ZIP codes also shrinks each one's physical footprint).
- Unique ZIP codes assigned to single large organizations, government agencies, or major universities exist outside the normal residential numbering pattern entirely, since they're assigned based on mail volume rather than geography.
Checking Any ZIP Code's Position in the System
If you want to see where a specific ZIP code falls within this national range, or explore ZIP codes at the state level to compare how numbering plays out regionally, our US ZIP code directory lets you browse by state and see the full range of codes assigned to each one. You can also look up any individual ZIP code directly to see its city, county, and coordinates through our ZIP code lookup.
The Bottom Line
The lowest ZIP codes in the country sit in the Northeast, largely due to Puerto Rico's and New England's position at the start of the original 1963 numbering sequence, while the highest belong to Alaska and the Pacific territories at the far end of that same sequence. It's a small but satisfying illustration of just how deliberately geographic the entire ZIP code system was designed to be from the very beginning, a structure covered in full in the history of the ZIP code system.
Related reading: How ZIP Codes Are Structured: A Complete Breakdown, The History of the ZIP Code System, Why Does One ZIP Code Cover Multiple Cities?