Validating City, County, State and Zip

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Does anybody know if it is possible to validate the City, County, State and Zip information when the user is filling out the application?  We need to transfer the new hire information to our Oracle HR system and there will be a failure if this information is not correct.  We would like to routinely extract this data from Oracle and use this data to either provide dropdown list to the users or at least validate what the users have entered into the textbox.  Has anyone ever done something like this?  If so how complex was the development configuration for this