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. | Garfield County | 3.3 |
| 2. | Petroleum County | 4.3 |
| 3. | Carter County | 5.3 |
| 4. | Liberty County | 5.5 |
| 5. | Wibaux County | 7.1 |
| 6. | Judith Basin County | 7.3 |
| 7. | Meagher County | 8.4 |
| 8. | McCone County | 8.6 |
| 9. | Fallon County | 9.2 |
| 10. | Prairie County | 9.8 |
| 11. | Granite County | 10.5 |
| 12. | Teton County | 11.7 |
| 13. | Sweet Grass County | 12.3 |
| 14. | Madison County | 12.7 |
| 15. | Fergus County | 14.1 |
| 16. | Carbon County | 14.1 |
| 17. | Broadwater County | 14.7 |
| 18. | Wheatland County | 14.7 |
| 19. | Jefferson County | 14.8 |
| 20. | Powder River County | 15.5 |
