I spent so much time on this! And super annoyed too in that I already had my custom "region" coded in my data source thinking I had to recreate manually in tableau. Like every time. This worked!. Also, HERO. :)
Will Tableau identify duplicate county names? For example, the county name of Santa Cruz is in AZ (Arizona) and CA (California). I have FIPS Codes that I like to use (State FIPS and County FIPS concatenated). Hopefully that will be the identifier that will bring in both counties. Is this true?