| | Duncan, OK | El Paso, TX | United States |
| Population | 22,664 | 676,395 | 329,725,481 |
| Female Population | 51.9% | 50.8% | 50.5% |
| Male Population | 48.1% | 49.2% | 49.5% |
| Median Age | 38.7 | 33.5 | 38.4 |
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| Population - 2010 | 23,438 | 650,482 | 309,327,143 |
| Population - 2000 | 22,505 | 563,662 | 285,036,114 |
| Population - 1990 | 21,732 | 515,342 | 251,960,433 |
| Pop. 2000 to Now | -1.1% | 20.9% | 15.6% |
| Pop. 1990 to Now | 2.4% | 32.3% | 30.8% |
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| Population Density | 528.6 | 2,628.2 | 93.4 |
| Land Area | 42.9 | 257.4 | 3,531,905.4 |
| Water Area | 4.9 | 0.9 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Duncan, OK | El Paso, TX | United States |
| Age 0 to 4 | 6.8% | 6.9% | 5.9% |
| Age 5 to 9 | 6.7% | 6.9% | 6.1% |
| Age 10 to 14 | 6.5% | 7.7% | 6.6% |
| Age 15 to 17 | 3.9% | 4.5% | 3.9% |
| Age 18 to 20 | 3.9% | 4.4% | 4.0% |
| Age 21 to 24 | 4.1% | 6.6% | 5.2% |
| Age 25 to 34 | 13.5% | 15.1% | 13.8% |
| Age 35 to 44 | 11.6% | 12.5% | 12.9% |
| Age 45 to 54 | 11.5% | 11.4% | 12.6% |
| Age 55 to 59 | 6.3% | 5.7% | 6.7% |
| Age 60 to 64 | 6.6% | 5.1% | 6.3% |
| Age 65 to 74 | 11.1% | 7.5% | 9.6% |
| Age 75 to 84 | 4.9% | 3.8% | 4.5% |
| Age 85 and over | 2.7% | 1.8% | 1.9% |
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| Race | | | |
| | Duncan, OK | El Paso, TX | United States |
| White | 75.3% | 12.4% | 59.4% |
| Black | 2.5% | 3.1% | 12.2% |
| Asian | 0.7% | 1.2% | 5.6% |
| Native American | 3.6% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.2% | 0.2% |
| Other | 0.3% | 0.1% | 0.4% |
| Two or More Races | 6.3% | 1.2% | 3.2% |
| Hispanic | 11.1% | 81.6% | 18.4% |
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| Marriage & Family | | | |
| | Duncan, OK | El Paso, TX | United States |
| Married Population | 51.3% | 48.4% | 49.8% |
| Currently Married | 49.5% | 44.8% | 48.0% |
| Married but Separated | 1.9% | 3.6% | 1.8% |
| Single Population | 48.7% | 51.6% | 50.2% |
| Never Married | 25.4% | 34.9% | 33.8% |
| Divorced | 14.0% | 11.1% | 10.8% |
| Widowed | 9.2% | 5.7% | 5.6% |
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| Household Size | 2.49 | 2.83 | 2.60 |
| Households | 8,938 | 236,708 | 124,010,992 |
| Family Households | 5,730 | 166,629 | 80,755,759 |
| Married couple, w/children | 29.9% | 30.6% | 30.5% |
| Married couple, no children | 43.4% | 33.2% | 42.9% |
| Non Family Households | 3,208 | 70,079 | 43,255,233 |
| Single householder, w/children | 17.6% | 21.9% | 15.8% |
| Single householder, no children | 9.1% | 14.3% | 10.8% |