Locations
| Name | Sites | Samples |
|---|---|---|
| Willacy County | 4 | 14 |
| Wilson County | 3 | 22 |
| Wilson County | 1 | 10 |
| Wilson County | 2 | 6 |
| Windsor County | 6 | 23 |
| Winkler County | 1 | 3 |
| Winn Parish | 1 | 1 |
| Winona County | 2 | 23 |
| Winston County | 1 | 3 |
| Wise County | 2 | 5 |
| Wood County | 13 | 33 |
| Wood County | 1 | 3 |
| Woodward County | 3 | 5 |
| Wright County | 1 | 2 |
| Wyoming County | 4 | 72 |
| Wythe County | 2 | 3 |
| Yadkin County | 2 | 7 |
| Yalobusha County | 2 | 6 |
| Yazoo County | 2 | 14 |
| Yell County | 2 | 4 |
| Yellow Medicine County | 1 | 4 |
| York County | 2 | 18 |
| York County | 1 | 9 |
| Young County | 1 | 41 |
| Zapata County | 5 | 53 |
| Zavala County | 10 | 37 |
| Ziebach County | 1 | 2 |
| Åland Islands | 1 | 6 |