The Diversity Index is a scale of 0 to 100 that represents the likelyhood that two persons, chosen at random from the same area, belong to different race or ethnic groups. If an area's entire population belongs to one race AND one ethnic group, then the area has zero diversity. An area's diversity index increases to 100 when the population is evenly divided into two or more race/ethnic groups.
| County | Diversity Index | |
|---|---|---|
| 1. | Lincoln County | 20.1 |
| 2. | Asotin County | 23.3 |
| 3. | Jefferson County | 24.2 |
| 4. | Pend Oreille County | 24.9 |
| 5. | Wahkiakum County | 25.7 |
| 6. | Skamania County | 27.2 |
| 7. | Garfield County | 27.5 |
| 8. | Stevens County | 28.3 |
| 9. | San Juan County | 28.9 |
| 10. | Columbia County | 32.1 |
| 11. | Spokane County | 33.2 |
| 12. | Kittitas County | 36.5 |
| 13. | Clallam County | 36.9 |
| 14. | Cowlitz County | 38.2 |
| 15. | Lewis County | 39.2 |
| 16. | Pacific County | 40.4 |
| 17. | Klickitat County | 41.3 |
| 18. | Whitman County | 41.8 |
| 19. | Island County | 42.8 |
| 20. | Mason County | 44.3 |
