Locations
| Name | Sites | Samples |
|---|---|---|
| Nash County | 1 | 3 |
| Nassau County | 8 | 12 |
| Nassau County | 2 | 4 |
| Natchitoches Parish | 8 | 23 |
| Navarro County | 4 | 12 |
| Nelson County | 2 | 5 |
| Neosho County | 2 | 3 |
| Netherlands | 228 | 1428 |
| New Hanover County | 5 | 8 |
| New Kent County | 3 | 5 |
| New York County | 1 | 2 |
| Newton County | 5 | 17 |
| Newton County | 1 | 1 |
| Newton County | 1 | 1 |
| Newton County | 2 | 5 |
| Niagara County | 2 | 2 |
| Nicollet County | 5 | 17 |
| Nigeria | 1 | 1 |
| Noble County | 4 | 11 |
| Nolan County | 1 | 1 |
| Northampton County | 5 | 24 |
| Northumberland County | 2 | 10 |
| Norton County | 2 | 3 |
| Norway | 19 | 35 |
| Oceana County | 1 | 1 |
| Ochiltree County | 7 | 20 |
| Oconee County | 2 | 3 |
| Oconee County | 2 | 4 |
| Okfuskee County | 2 | 2 |
| Okmulgee County | 1 | 1 |