Locations
| Name | Sites | Samples |
|---|---|---|
| Republic County | 1 | 9 |
| Rhea County | 3 | 22 |
| Richland County | 1 | 11 |
| Richland Parish | 3 | 11 |
| Richmond County | 5 | 59 |
| Richmond County | 4 | 24 |
| Richmond County | 1 | 3 |
| Ritchie County | 0 | 0 |
| Roane County | 6 | 29 |
| Roanoke County | 10 | 59 |
| Robertson County | 1 | 4 |
| Robertson County | 2 | 3 |
| Robeson County | 1 | 1 |
| Rockbridge County | 5 | 18 |
| Rockdale County | 3 | 8 |
| Rockingham County | 8 | 38 |
| Rockingham County | 2 | 4 |
| Rockwall County | 1 | 2 |
| Romania | 104 | 287 |
| Roscommon County | 3 | 24 |
| Runnels County | 3 | 25 |
| Rush County | 2 | 4 |
| Rusk County | 17 | 124 |
| Russell County | 4 | 16 |
| Russell County | 1 | 5 |
| Russia | 576 | 1596 |
| Rutherford County | 2 | 3 |
| Sabine County | 2 | 2 |
| Sabine Parish | 2 | 7 |
| Saline County | 3 | 8 |