Locations
| Name | Sites | Samples |
|---|---|---|
| Oktibbeha County | 17 | 65 |
| Oneida County | 4 | 4 |
| Onslow County | 13 | 53 |
| Ontonagon County | 1 | 2 |
| Orange County | 2 | 4 |
| Orange County | 2 | 4 |
| Orange County | 4 | 6 |
| Orange County | 2 | 8 |
| Orange County | 6 | 13 |
| Orange County | 1 | 4 |
| Orleans Parish | 7 | 26 |
| Osage County | 1 | 5 |
| Osage County | 12 | 39 |
| Osceola County | 1 | 4 |
| Otoe County | 2 | 6 |
| Ottawa County | 1 | 1 |
| Ouachita County | 1 | 10 |
| Owen County | 1 | 3 |
| Page County | 3 | 12 |
| Palm Beach County | 10 | 71 |
| Panama | 11 | 51 |
| Panola County | 2 | 28 |
| Paraguay | 2 | 2 |
| Parke County | 2 | 5 |
| Parker County | 2 | 3 |
| Patrick County | 3 | 7 |
| Pawnee County | 3 | 3 |
| Pawnee County | 1 | 2 |
| Pearl River County | 1 | 6 |
| Perry County | 3 | 17 |