Counties, Cities and ZIP Codes: How US Geography Fits Together

Geography  |  April 8, 2026  |  2 min read

People often assume a ZIP code belongs to one city, and a city sits in one county. In practice, these layers overlap in messy ways.

States and counties

All states are divided into counties or county-equivalents. Louisiana calls them parishes and Alaska uses boroughs and census areas. A few cities, such as those in Virginia, are independent of any county.

Cities and places

A city is a legal municipality. The city name in a mailing address, however, is the post office name, which can differ from the municipality where the home actually sits. Many suburban addresses carry the name of a nearby larger town.

ZIP codes

ZIP codes follow mail delivery routes. One ZIP can cover parts of several towns, and a large city can contain dozens of ZIP codes. Some ZIPs even cross county lines.

Why this matters

• Sales tax often depends on the exact location, not just the ZIP code.
• Voting districts and school zones ignore ZIP boundaries.
• Analytics grouped by ZIP may not match city or county totals.

Practical tips

Store city, county, state and ZIP as separate fields. When accuracy matters, use a geocoding or tax service rather than guessing from the ZIP alone. For testing, pick addresses from state and city pages that show the county, so you can check county-based rules.