How ZIP Codes Are Assigned: The First Three Digits Explained
Every five-digit ZIP code carries a rough map of the country inside it. Read from left to right, the digits move from a broad region down to a local post office or delivery area.
The first digit: a group of states
ZIP codes start at 0 in the Northeast and climb to 9 on the West Coast.
| First digit | States (main examples) |
|---|---|
| 0 | CT, MA, ME, NH, NJ, RI, VT, Puerto Rico |
| 1 | DE, NY, PA |
| 2 | DC, MD, NC, SC, VA, WV |
| 3 | AL, FL, GA, MS, TN |
| 4 | IN, KY, MI, OH |
| 5 | IA, MN, MT, ND, SD, WI |
| 6 | IL, KS, MO, NE |
| 7 | AR, LA, OK, TX |
| 8 | AZ, CO, ID, NM, NV, UT, WY |
| 9 | AK, CA, HI, OR, WA |
The first three digits: a sectional center
The first three digits identify a sectional center facility, a processing plant that sorts mail for a group of nearby post offices. For example, codes starting with 100 to 102 belong to Manhattan, while 606 covers much of Chicago.
The last two digits: the delivery area
The final two digits point to a specific post office or delivery zone inside the sectional center. In larger cities they often map to neighborhoods.
Three kinds of ZIP codes
- Standard ZIP codes cover geographic delivery areas.
- PO Box ZIP codes serve only post office boxes at one facility.
- Unique ZIP codes belong to a single high-volume address, such as a government agency, a university or a large company.
Why ZIP codes are not boundaries
ZIP codes are delivery routes, not official borders. One code can cross city and even county lines, and one city can have dozens of codes. That is why a city name and ZIP code do not always match what people expect, and why address tools always check them together.
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