How to list the ZIP codes in a city, county or congressional district

Ask for the ZIP codes linked to the city, county or district, with each ZIP's share of residents inside it. That lets you keep ZIPs that are mostly inside and drop ones that only clip the edge, which a plain list can't tell you.

Who this is for

Direct mail and local marketing
Service-area and delivery planning
Grant and program eligibility

Ask your agent

With Boundary Atlas added to Claude, ChatGPT, Cursor or Codex (free, no key; how):

List the ZIP codes that are at least half inside Houston, TX, with the share of each ZIP's residents in the city.

Step by step

Find the ID. search_geographies(query="Houston", level="place", region="TX") gives us:place:4835000.
List the ZIPs. related_geographies(id="us:place:4835000", level="zcta", min_weight=0.5).
Map them. get_boundaries(id="us:zcta:<ZIP>") for each, or ask the agent for one GeoJSON file.

Live example

Houston, TX touches 130 ZIP codes; 70 have at least half of their residents inside the city. The first 40 of those:

related_geographies(id="us:place:4835000", level="zcta", min_weight=0.5)

Things to know

Shares are of 2020 residents; a ZIP of offices or warehouses can read 0%.
City boundaries are as of January 1, 2025.

Questions

How many ZIP codes are in a city?

It depends on the cut-off: count every ZIP touching the city, or only ZIPs mostly inside it. Boundary Atlas gives the share for each, so you can choose.