The US County Border option is checked, but the map does not show them... And the option is greyed out and will not let me click on it.
What version of tableau are your using and can you share what you see or even the workbook. You should have this option available.
One thing this happens when your map is zoomed out. Zoom out (click + on the zoom controls) your map and you should see the counties.
Hope this helps
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