How to override the city derived automatically by R12/Vertex for a specific US zip code.

We are having issues when entering a supplier site address.  This is for US.  When we enter the zip code of 60642 (which is clearly Chicago, IL)  and type Chicago, IL in the city state and then save we get an error message "These address elements are not validated: POSTAL_CODE. Correct the invalid elements, or continue and save the invalid address".  We can save the address but the city name always populates with Eppeville, IL and there is no way to update it to Chicago, IL.  The supplier address screen produces a "Suggestion" LOV which allows us to pick Chicago,