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You should just need to drop your Census tract ID dimension onto Detail and that will disaggregate the polygons. By default Tableau aggregates everything (including polygon geometries), so to disaggregate you just have to add a level of detail that tells Tableau how to identify the unique polygons. The Census tract ID or GEOID should do that for this dataset. In the image below the 'Aggregate Measures' is ON and you can still see the unique polygons, but the attributes are aggregated for each unique polygon.
That worked like a charm!