You can identify constituents within a certain Zip Code radius by querying based upon partial Zip Code. Zip Codes in nearby areas normally overlap the first few digits, so you can build a Query to identify constituents with Zip Codes that begin with those first few digits.

To do this, you will want to:
  1. Go to Data Management > Query
  2. Click Create a new Query
  3. Add the Name, Description, and Security Category as needed and click Save
  4. Select "Address" for the Field Type and "ZIP" for the Field
  5. Click Add Field Clause and select "Home Address" "begins with" "XXX" (where XXX is the desired number of zip code digits"
  6. Click Save
  7. Click Save Query and Run Query
You can then add the query results to a group and use that group for an email's audience.