Multi-County Zip Code Data (MCZ):
The MCZ file contains a zip code, plus the possible counties in which
the zip code may cross over. It also has an estimated percentage of
the zip code that falls within that county.
This file is ideal for those applications where you need to know if
a Zip Code is entirely in one county or not, such as:
- Tax calculations
- Insurance rate calculations
- HMO coverage area determination
- Sales territory assignments
- Fraud detection
This file is currently updated about every 4 months. Overall, the data
seems to be very accurate, but we've found some records which have alternative
county names that may not be correct, these usually are coded as covering
only one percent or less of the Zip Code and can be ignored.