| | Sidney, IA | Washington, DC | United States |
| Population | 961 | 683,154 | 329,725,481 |
| Female Population | 54.0% | 52.4% | 50.5% |
| Male Population | 46.0% | 47.7% | 49.5% |
| Median Age | 38.8 | 34.3 | 38.4 |
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| Population - 2010 | 1,136 | 605,282 | 309,327,143 |
| Population - 2000 | 1,300 | 572,059 | 285,036,114 |
| Population - 1990 | 1,253 | 606,900 | 251,960,433 |
| Pop. 2000 to Now | -21.9% | 24.6% | 15.6% |
| Pop. 1990 to Now | -18.9% | 17.5% | 30.8% |
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| Population Density | 696.4 | 11,174.3 | 93.4 |
| Land Area | 1.4 | 61.1 | 3,531,905.4 |
| Water Area | 0.0 | 7.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Sidney, IA | Washington, DC | United States |
| Age 0 to 4 | 6.8% | 6.3% | 5.9% |
| Age 5 to 9 | 10.4% | 5.1% | 6.1% |
| Age 10 to 14 | 4.6% | 4.6% | 6.6% |
| Age 15 to 17 | 3.0% | 2.3% | 3.9% |
| Age 18 to 20 | 1.4% | 4.5% | 4.0% |
| Age 21 to 24 | 6.5% | 5.8% | 5.2% |
| Age 25 to 34 | 10.3% | 22.8% | 13.8% |
| Age 35 to 44 | 10.2% | 15.6% | 12.9% |
| Age 45 to 54 | 9.9% | 10.8% | 12.6% |
| Age 55 to 59 | 4.7% | 5.2% | 6.7% |
| Age 60 to 64 | 7.7% | 4.9% | 6.3% |
| Age 65 to 74 | 14.6% | 7.2% | 9.6% |
| Age 75 to 84 | 5.7% | 3.5% | 4.5% |
| Age 85 and over | 4.4% | 1.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Sidney, IA | Washington, DC | United States |
| White | 91.1% | 36.7% | 59.4% |
| Black | 0.6% | 43.9% | 12.2% |
| Asian | 0.0% | 4.0% | 5.6% |
| Native American | 0.4% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.5% | 0.4% |
| Two or More Races | 3.9% | 3.5% | 3.2% |
| Hispanic | 4.1% | 11.3% | 18.4% |
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| Marriage & Family | | | |
| | Sidney, IA | Washington, DC | United States |
| Married Population | 44.1% | 32.6% | 49.8% |
| Currently Married | 42.7% | 30.9% | 48.0% |
| Married but Separated | 1.5% | 1.7% | 1.8% |
| Single Population | 55.9% | 67.4% | 50.2% |
| Never Married | 24.7% | 55.8% | 33.8% |
| Divorced | 18.6% | 8.2% | 10.8% |
| Widowed | 12.5% | 3.5% | 5.6% |
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| Household Size | 2.36 | 2.08 | 2.60 |
| Households | 387 | 310,104 | 124,010,992 |
| Family Households | 189 | 131,196 | 80,755,759 |
| Married couple, w/children | 31.2% | 24.1% | 30.5% |
| Married couple, no children | 40.2% | 36.8% | 42.9% |
| Non Family Households | 198 | 178,908 | 43,255,233 |
| Single householder, w/children | 15.3% | 22.8% | 15.8% |
| Single householder, no children | 13.2% | 16.2% | 10.8% |