| | Enid, OK | Duncan, OK | United States |
| Population | 51,129 | 22,664 | 329,725,481 |
| Female Population | 49.4% | 51.9% | 50.5% |
| Male Population | 50.6% | 48.1% | 49.5% |
| Median Age | 34.9 | 38.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 49,534 | 23,438 | 309,327,143 |
| Population - 2000 | 47,045 | 22,505 | 285,036,114 |
| Population - 1990 | 45,309 | 21,732 | 251,960,433 |
| Pop. 2000 to Now | 5.3% | -1.1% | 15.6% |
| Pop. 1990 to Now | 9.3% | 2.4% | 30.8% |
| space4 | | | |
| Population Density | 691.3 | 528.6 | 93.4 |
| Land Area | 74.0 | 42.9 | 3,531,905.4 |
| Water Area | 0.1 | 4.9 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Enid, OK | Duncan, OK | United States |
| Age 0 to 4 | 7.0% | 6.8% | 5.9% |
| Age 5 to 9 | 6.8% | 6.7% | 6.1% |
| Age 10 to 14 | 6.5% | 6.5% | 6.6% |
| Age 15 to 17 | 4.8% | 3.9% | 3.9% |
| Age 18 to 20 | 4.7% | 3.9% | 4.0% |
| Age 21 to 24 | 5.7% | 4.1% | 5.2% |
| Age 25 to 34 | 14.6% | 13.5% | 13.8% |
| Age 35 to 44 | 12.0% | 11.6% | 12.9% |
| Age 45 to 54 | 10.4% | 11.5% | 12.6% |
| Age 55 to 59 | 6.2% | 6.3% | 6.7% |
| Age 60 to 64 | 6.5% | 6.6% | 6.3% |
| Age 65 to 74 | 7.7% | 11.1% | 9.6% |
| Age 75 to 84 | 4.8% | 4.9% | 4.5% |
| Age 85 and over | 2.2% | 2.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Enid, OK | Duncan, OK | United States |
| White | 69.1% | 75.3% | 59.4% |
| Black | 2.6% | 2.5% | 12.2% |
| Asian | 1.3% | 0.7% | 5.6% |
| Native American | 1.8% | 3.6% | 0.6% |
| Hawaiian, Pacific Islander | 4.5% | 0.1% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 5.4% | 6.3% | 3.2% |
| Hispanic | 15.3% | 11.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Enid, OK | Duncan, OK | United States |
| Married Population | 48.0% | 51.3% | 49.8% |
| Currently Married | 47.0% | 49.5% | 48.0% |
| Married but Separated | 1.0% | 1.9% | 1.8% |
| Single Population | 52.0% | 48.7% | 50.2% |
| Never Married | 32.7% | 25.4% | 33.8% |
| Divorced | 12.7% | 14.0% | 10.8% |
| Widowed | 6.5% | 9.2% | 5.6% |
| space5 | | | |
| Household Size | 2.55 | 2.49 | 2.60 |
| Households | 19,428 | 8,938 | 124,010,992 |
| Family Households | 12,100 | 5,730 | 80,755,759 |
| Married couple, w/children | 25.5% | 29.9% | 30.5% |
| Married couple, no children | 48.7% | 43.4% | 42.9% |
| Non Family Households | 7,328 | 3,208 | 43,255,233 |
| Single householder, w/children | 16.9% | 17.6% | 15.8% |
| Single householder, no children | 9.0% | 9.1% | 10.8% |