| | De Smet, SD | Mitchell, SD | United States |
| Population | 1,128 | 15,677 | 329,725,481 |
| Female Population | 48.0% | 50.9% | 50.5% |
| Male Population | 52.0% | 49.1% | 49.5% |
| Median Age | 45.3 | 38.5 | 38.4 |
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| Population - 2010 | 1,087 | 15,265 | 309,327,143 |
| Population - 2000 | 1,164 | 14,558 | 285,036,114 |
| Population - 1990 | 1,172 | 13,798 | 251,960,433 |
| Pop. 2000 to Now | -9.2% | 7.8% | 15.6% |
| Pop. 1990 to Now | -9.8% | 13.8% | 30.8% |
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| Population Density | 974.1 | 1,366.7 | 93.4 |
| Land Area | 1.2 | 11.5 | 3,531,905.4 |
| Water Area | 0.0 | 1.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | De Smet, SD | Mitchell, SD | United States |
| Age 0 to 4 | 4.1% | 5.6% | 5.9% |
| Age 5 to 9 | 7.4% | 6.5% | 6.1% |
| Age 10 to 14 | 7.9% | 5.9% | 6.6% |
| Age 15 to 17 | 4.1% | 4.1% | 3.9% |
| Age 18 to 20 | 2.1% | 4.4% | 4.0% |
| Age 21 to 24 | 2.7% | 6.0% | 5.2% |
| Age 25 to 34 | 7.4% | 14.4% | 13.8% |
| Age 35 to 44 | 14.0% | 10.7% | 12.9% |
| Age 45 to 54 | 8.8% | 8.9% | 12.6% |
| Age 55 to 59 | 4.5% | 7.7% | 6.7% |
| Age 60 to 64 | 7.1% | 5.6% | 6.3% |
| Age 65 to 74 | 12.6% | 10.7% | 9.6% |
| Age 75 to 84 | 8.2% | 6.9% | 4.5% |
| Age 85 and over | 9.3% | 2.7% | 1.9% |
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| Race | | | |
| | De Smet, SD | Mitchell, SD | United States |
| White | 98.2% | 88.4% | 59.4% |
| Black | 0.0% | 0.8% | 12.2% |
| Asian | 0.0% | 1.2% | 5.6% |
| Native American | 0.7% | 2.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 1.1% | 3.1% | 3.2% |
| Hispanic | 0.0% | 4.2% | 18.4% |
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| Marriage & Family | | | |
| | De Smet, SD | Mitchell, SD | United States |
| Married Population | 56.5% | 49.8% | 49.8% |
| Currently Married | 55.9% | 47.8% | 48.0% |
| Married but Separated | 0.5% | 2.0% | 1.8% |
| Single Population | 43.5% | 50.2% | 50.2% |
| Never Married | 21.5% | 32.6% | 33.8% |
| Divorced | 12.1% | 9.6% | 10.8% |
| Widowed | 9.9% | 8.0% | 5.6% |
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| Household Size | 2.53 | 2.09 | 2.60 |
| Households | 429 | 7,031 | 124,010,992 |
| Family Households | 271 | 3,805 | 80,755,759 |
| Married couple, w/children | 34.3% | 22.2% | 30.5% |
| Married couple, no children | 48.7% | 56.1% | 42.9% |
| Non Family Households | 158 | 3,226 | 43,255,233 |
| Single householder, w/children | 7.7% | 16.4% | 15.8% |
| Single householder, no children | 9.2% | 5.3% | 10.8% |