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.