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. | Nevada County | 33.6 |
| 2. | Plumas County | 36.7 |
| 3. | Sierra County | 36.9 |
| 4. | Trinity County | 37.8 |
| 5. | Calaveras County | 42.1 |
| 6. | Shasta County | 42.6 |
| 7. | Mariposa County | 43.1 |
| 8. | Tuolumne County | 43.9 |
| 9. | El Dorado County | 45.5 |
| 10. | Amador County | 46.2 |
| 11. | Siskiyou County | 49.1 |
| 12. | Modoc County | 49.2 |
| 13. | Humboldt County | 51.1 |
| 14. | Placer County | 52.5 |
| 15. | Marin County | 55.2 |
| 16. | Butte County | 55.6 |
| 17. | San Luis Obispo County | 58.1 |
| 18. | Alpine County | 59.4 |
| 19. | Lake County | 61.6 |
| 20. | Mono County | 62.8 |
