| | Holly Springs, NC | Cary, NC | United States |
| Population | 40,198 | 171,603 | 329,725,481 |
| Female Population | 52.9% | 50.6% | 50.5% |
| Male Population | 47.1% | 49.4% | 49.5% |
| Median Age | 35.5 | 39.1 | 38.4 |
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| Population - 2010 | 24,962 | 137,116 | 309,327,143 |
| Population - 2000 | 9,192 | 94,536 | 285,036,114 |
| Population - 1990 | 908 | 43,858 | 251,960,433 |
| Pop. 2000 to Now | 333.9% | 83.6% | 15.6% |
| Pop. 1990 to Now | 4,292.3% | 295.8% | 30.8% |
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| Population Density | 2,467.5 | 2,995.2 | 93.4 |
| Land Area | 16.3 | 57.3 | 3,531,905.4 |
| Water Area | 0.1 | 1.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Holly Springs, NC | Cary, NC | United States |
| Age 0 to 4 | 6.8% | 5.5% | 5.9% |
| Age 5 to 9 | 8.6% | 7.3% | 6.1% |
| Age 10 to 14 | 13.1% | 7.9% | 6.6% |
| Age 15 to 17 | 5.6% | 4.7% | 3.9% |
| Age 18 to 20 | 2.5% | 2.8% | 4.0% |
| Age 21 to 24 | 2.7% | 4.0% | 5.2% |
| Age 25 to 34 | 10.0% | 11.6% | 13.8% |
| Age 35 to 44 | 18.1% | 15.6% | 12.9% |
| Age 45 to 54 | 16.5% | 15.7% | 12.6% |
| Age 55 to 59 | 4.5% | 6.5% | 6.7% |
| Age 60 to 64 | 3.5% | 5.8% | 6.3% |
| Age 65 to 74 | 5.9% | 7.7% | 9.6% |
| Age 75 to 84 | 1.6% | 3.6% | 4.5% |
| Age 85 and over | 0.5% | 1.1% | 1.9% |
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| Race | | | |
| | Holly Springs, NC | Cary, NC | United States |
| White | 75.4% | 59.6% | 59.4% |
| Black | 9.7% | 7.7% | 12.2% |
| Asian | 5.6% | 20.2% | 5.6% |
| Native American | 0.2% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.7% | 0.6% | 0.4% |
| Two or More Races | 3.0% | 3.4% | 3.2% |
| Hispanic | 5.4% | 8.3% | 18.4% |
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| Marriage & Family | | | |
| | Holly Springs, NC | Cary, NC | United States |
| Married Population | 67.2% | 62.5% | 49.8% |
| Currently Married | 66.1% | 60.7% | 48.0% |
| Married but Separated | 1.1% | 1.8% | 1.8% |
| Single Population | 32.8% | 37.5% | 50.2% |
| Never Married | 22.7% | 25.7% | 33.8% |
| Divorced | 8.0% | 8.0% | 10.8% |
| Widowed | 2.0% | 3.8% | 5.6% |
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| Household Size | 3.09 | 2.66 | 2.60 |
| Households | 12,988 | 64,512 | 124,010,992 |
| Family Households | 10,804 | 46,511 | 80,755,759 |
| Married couple, w/children | 54.6% | 42.4% | 30.5% |
| Married couple, no children | 30.1% | 41.9% | 42.9% |
| Non Family Households | 2,184 | 18,001 | 43,255,233 |
| Single householder, w/children | 13.0% | 10.4% | 15.8% |
| Single householder, no children | 2.3% | 5.3% | 10.8% |