Understanding US Zip Codes

In the United States there are States and Provinces.  These States and Provinces have Cities.  The same city name may be used in different states.  For instance, Springfield, MO (Missouri) and Springfield, IL (Illinois).  A single city may be covered by more than one zip code.  A zip code may span states.

The graphic above shows 13 of the 16 Zip codes that are used for Springfield, MO.  For Springfield, IL, different Zip codes are used.  Here 7 of Springfield, IL 36 zip codes are shown.

Reference

http://zipcode.org/ 
http://zipcode.org/city/MO/SPRINGFIELD
http://zipcode.org/city/IL/SPRINGFIELD