| | Gillette, WY | Williston, ND | United States |
| Population | 33,047 | 27,368 | 329,725,481 |
| Female Population | 48.2% | 45.7% | 50.5% |
| Male Population | 51.8% | 54.3% | 49.5% |
| Median Age | 32.3 | 30.9 | 38.4 |
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| Population - 2010 | 31,558 | 16,081 | 309,327,143 |
| Population - 2000 | 19,646 | 12,512 | 285,036,114 |
| Population - 1990 | 17,635 | 13,131 | 251,960,433 |
| Pop. 2000 to Now | 64.0% | 137.8% | 15.6% |
| Pop. 1990 to Now | 82.7% | 126.6% | 30.8% |
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| Population Density | 1,437.7 | 1,181.3 | 93.4 |
| Land Area | 23.0 | 23.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Gillette, WY | Williston, ND | United States |
| Age 0 to 4 | 8.2% | 9.4% | 5.9% |
| Age 5 to 9 | 9.9% | 7.7% | 6.1% |
| Age 10 to 14 | 8.4% | 7.9% | 6.6% |
| Age 15 to 17 | 4.0% | 3.7% | 3.9% |
| Age 18 to 20 | 3.6% | 2.6% | 4.0% |
| Age 21 to 24 | 3.9% | 6.1% | 5.2% |
| Age 25 to 34 | 16.4% | 21.1% | 13.8% |
| Age 35 to 44 | 14.0% | 16.4% | 12.9% |
| Age 45 to 54 | 8.6% | 9.3% | 12.6% |
| Age 55 to 59 | 7.3% | 4.5% | 6.7% |
| Age 60 to 64 | 5.9% | 3.5% | 6.3% |
| Age 65 to 74 | 6.8% | 4.5% | 9.6% |
| Age 75 to 84 | 2.4% | 1.2% | 4.5% |
| Age 85 and over | 0.7% | 1.9% | 1.9% |
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| Race | | | |
| | Gillette, WY | Williston, ND | United States |
| White | 84.9% | 71.9% | 59.4% |
| Black | 0.4% | 6.6% | 12.2% |
| Asian | 0.1% | 1.5% | 5.6% |
| Native American | 0.8% | 1.8% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.3% | 0.2% |
| Other | 0.0% | 0.8% | 0.4% |
| Two or More Races | 3.8% | 5.0% | 3.2% |
| Hispanic | 10.1% | 12.0% | 18.4% |
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| Marriage & Family | | | |
| | Gillette, WY | Williston, ND | United States |
| Married Population | 58.9% | 49.1% | 49.8% |
| Currently Married | 56.7% | 48.5% | 48.0% |
| Married but Separated | 2.2% | 0.7% | 1.8% |
| Single Population | 41.1% | 50.9% | 50.2% |
| Never Married | 25.7% | 32.5% | 33.8% |
| Divorced | 11.6% | 14.6% | 10.8% |
| Widowed | 3.8% | 3.7% | 5.6% |
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| Household Size | 2.73 | 2.40 | 2.60 |
| Households | 11,954 | 11,216 | 124,010,992 |
| Family Households | 8,301 | 6,376 | 80,755,759 |
| Married couple, w/children | 39.1% | 35.6% | 30.5% |
| Married couple, no children | 38.4% | 38.7% | 42.9% |
| Non Family Households | 3,653 | 4,840 | 43,255,233 |
| Single householder, w/children | 19.9% | 21.8% | 15.8% |
| Single householder, no children | 2.7% | 3.8% | 10.8% |