| | Duncan, SC | Rock Hill, SC | United States |
| Population | 3,937 | 72,883 | 329,725,481 |
| Female Population | 54.1% | 54.1% | 50.5% |
| Male Population | 46.0% | 45.9% | 49.5% |
| Median Age | 30.5 | 34.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,192 | 66,872 | 309,327,143 |
| Population - 2000 | 2,870 | 49,765 | 285,036,114 |
| Population - 1990 | 2,152 | 41,643 | 251,960,433 |
| Pop. 2000 to Now | 29.4% | 53.4% | 15.6% |
| Pop. 1990 to Now | 72.6% | 83.3% | 30.8% |
| space4 | | | |
| Population Density | 826.8 | 1,916.6 | 93.4 |
| Land Area | 4.8 | 38.0 | 3,531,905.4 |
| Water Area | 0.1 | 0.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Duncan, SC | Rock Hill, SC | United States |
| Age 0 to 4 | 7.5% | 6.4% | 5.9% |
| Age 5 to 9 | 10.6% | 6.4% | 6.1% |
| Age 10 to 14 | 6.2% | 6.3% | 6.6% |
| Age 15 to 17 | 1.6% | 4.0% | 3.9% |
| Age 18 to 20 | 1.4% | 5.9% | 4.0% |
| Age 21 to 24 | 2.3% | 6.8% | 5.2% |
| Age 25 to 34 | 28.4% | 15.7% | 13.8% |
| Age 35 to 44 | 11.9% | 11.8% | 12.9% |
| Age 45 to 54 | 7.7% | 11.8% | 12.6% |
| Age 55 to 59 | 6.3% | 5.5% | 6.7% |
| Age 60 to 64 | 5.9% | 5.6% | 6.3% |
| Age 65 to 74 | 6.7% | 8.7% | 9.6% |
| Age 75 to 84 | 0.6% | 3.6% | 4.5% |
| Age 85 and over | 2.8% | 1.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Duncan, SC | Rock Hill, SC | United States |
| White | 52.7% | 51.1% | 59.4% |
| Black | 33.3% | 38.5% | 12.2% |
| Asian | 0.0% | 1.9% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.4% | 0.4% |
| Two or More Races | 4.0% | 2.2% | 3.2% |
| Hispanic | 9.9% | 5.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Duncan, SC | Rock Hill, SC | United States |
| Married Population | 39.9% | 42.7% | 49.8% |
| Currently Married | 35.7% | 39.8% | 48.0% |
| Married but Separated | 4.2% | 2.9% | 1.8% |
| Single Population | 60.1% | 57.3% | 50.2% |
| Never Married | 33.7% | 40.9% | 33.8% |
| Divorced | 13.7% | 10.8% | 10.8% |
| Widowed | 12.7% | 5.7% | 5.6% |
| space5 | | | |
| Household Size | 2.50 | 2.37 | 2.60 |
| Households | 1,565 | 29,588 | 124,010,992 |
| Family Households | 961 | 17,390 | 80,755,759 |
| Married couple, w/children | 24.8% | 24.7% | 30.5% |
| Married couple, no children | 27.5% | 37.9% | 42.9% |
| Non Family Households | 604 | 12,198 | 43,255,233 |
| Single householder, w/children | 38.1% | 24.2% | 15.8% |
| Single householder, no children | 9.7% | 13.2% | 10.8% |