Hi Ibrahima Kaba,
A couple of things that might help. Tableau today, supports a definition of second level administrative units in the UK, which include Counties, Unitary Authorities and Local Authority Districts (incl. ONS and GSS codes). If that is not what you are looking for (I know not all Counties will map in Tableau if you are expecting something like 380 counties), then I would suggest downloading the shapefile that you are looking for from the Ordnance Survey or other geospatial portal that you prefer because Tableau v. 10.2 (currently available for Beta testing) will support connecting directing to spatial files, including Shapefiles.