| | Belle Fourche, SD | Great Falls, MT | United States |
| Population | 5,561 | 60,381 | 329,725,481 |
| Female Population | 50.3% | 50.6% | 50.5% |
| Male Population | 49.7% | 49.4% | 49.5% |
| Median Age | 38.7 | 39 | 38.4 |
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| Population - 2010 | 5,614 | 59,239 | 309,327,143 |
| Population - 2000 | 4,565 | 56,690 | 285,036,114 |
| Population - 1990 | 4,335 | 55,097 | 251,960,433 |
| Pop. 2000 to Now | 25.8% | 2.9% | 15.6% |
| Pop. 1990 to Now | 32.5% | 5.9% | 30.8% |
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| Population Density | 628.5 | 2,630.3 | 93.4 |
| Land Area | 8.8 | 23.0 | 3,531,905.4 |
| Water Area | 0.1 | 0.5 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Belle Fourche, SD | Great Falls, MT | United States |
| Age 0 to 4 | 4.6% | 5.8% | 5.9% |
| Age 5 to 9 | 7.2% | 6.1% | 6.1% |
| Age 10 to 14 | 5.5% | 6.1% | 6.6% |
| Age 15 to 17 | 5.4% | 3.6% | 3.9% |
| Age 18 to 20 | 4.6% | 3.5% | 4.0% |
| Age 21 to 24 | 4.7% | 5.2% | 5.2% |
| Age 25 to 34 | 12.1% | 14.3% | 13.8% |
| Age 35 to 44 | 12.2% | 11.7% | 12.9% |
| Age 45 to 54 | 13.2% | 11.3% | 12.6% |
| Age 55 to 59 | 5.4% | 6.4% | 6.7% |
| Age 60 to 64 | 9.4% | 6.6% | 6.3% |
| Age 65 to 74 | 7.8% | 10.7% | 9.6% |
| Age 75 to 84 | 5.7% | 5.7% | 4.5% |
| Age 85 and over | 2.5% | 2.9% | 1.9% |
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| Race | | | |
| | Belle Fourche, SD | Great Falls, MT | United States |
| White | 87.0% | 83.1% | 59.4% |
| Black | 0.0% | 1.1% | 12.2% |
| Asian | 0.4% | 0.8% | 5.6% |
| Native American | 1.4% | 4.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.5% | 0.0% | 0.2% |
| Other | 0.6% | 0.1% | 0.4% |
| Two or More Races | 3.1% | 5.1% | 3.2% |
| Hispanic | 7.0% | 5.3% | 18.4% |
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| Marriage & Family | | | |
| | Belle Fourche, SD | Great Falls, MT | United States |
| Married Population | 49.0% | 47.0% | 49.8% |
| Currently Married | 47.5% | 45.4% | 48.0% |
| Married but Separated | 1.4% | 1.6% | 1.8% |
| Single Population | 51.0% | 53.0% | 50.2% |
| Never Married | 29.0% | 30.6% | 33.8% |
| Divorced | 17.0% | 14.9% | 10.8% |
| Widowed | 5.0% | 7.5% | 5.6% |
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| Household Size | 2.35 | 2.30 | 2.60 |
| Households | 2,327 | 25,548 | 124,010,992 |
| Family Households | 1,302 | 14,681 | 80,755,759 |
| Married couple, w/children | 41.8% | 23.6% | 30.5% |
| Married couple, no children | 41.5% | 48.7% | 42.9% |
| Non Family Households | 1,025 | 10,867 | 43,255,233 |
| Single householder, w/children | 9.8% | 19.3% | 15.8% |
| Single householder, no children | 6.9% | 8.4% | 10.8% |