| | Mount Holly, NJ | Clark, NJ | United States |
| Population | 9,918 | 15,445 | 329,725,481 |
| Female Population | 43.3% | 49.4% | 50.5% |
| Male Population | 56.7% | 50.6% | 49.5% |
| Median Age | 35.2 | 42.5 | 38.4 |
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| Population - 2010 | 9,554 | 14,762 | 309,327,143 |
| Population - 2000 | 10,728 | 14,597 | 285,036,114 |
| Population - 1990 | 10,639 | 14,629 | 251,960,433 |
| Pop. 2000 to Now | -11.2% | 8.5% | 15.6% |
| Pop. 1990 to Now | -10.5% | 8.3% | 30.8% |
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| Population Density | 3,534.6 | 3,587.7 | 93.4 |
| Land Area | 2.8 | 4.3 | 3,531,905.4 |
| Water Area | 0.0 | 0.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Mount Holly, NJ | Clark, NJ | United States |
| Age 0 to 4 | 4.6% | 5.7% | 5.9% |
| Age 5 to 9 | 5.3% | 7.8% | 6.1% |
| Age 10 to 14 | 7.3% | 4.8% | 6.6% |
| Age 15 to 17 | 4.3% | 3.1% | 3.9% |
| Age 18 to 20 | 4.1% | 2.3% | 4.0% |
| Age 21 to 24 | 4.8% | 5.0% | 5.2% |
| Age 25 to 34 | 19.1% | 12.5% | 13.8% |
| Age 35 to 44 | 13.8% | 13.4% | 12.9% |
| Age 45 to 54 | 11.6% | 11.4% | 12.6% |
| Age 55 to 59 | 7.5% | 6.4% | 6.7% |
| Age 60 to 64 | 5.5% | 7.3% | 6.3% |
| Age 65 to 74 | 7.4% | 10.7% | 9.6% |
| Age 75 to 84 | 3.4% | 6.2% | 4.5% |
| Age 85 and over | 1.3% | 3.5% | 1.9% |
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| Race | | | |
| | Mount Holly, NJ | Clark, NJ | United States |
| White | 53.4% | 82.3% | 59.4% |
| Black | 22.4% | 2.2% | 12.2% |
| Asian | 3.2% | 3.7% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.4% | 0.4% |
| Two or More Races | 6.0% | 1.2% | 3.2% |
| Hispanic | 14.6% | 10.3% | 18.4% |
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| Marriage & Family | | | |
| | Mount Holly, NJ | Clark, NJ | United States |
| Married Population | 41.6% | 56.9% | 49.8% |
| Currently Married | 38.8% | 55.7% | 48.0% |
| Married but Separated | 2.8% | 1.2% | 1.8% |
| Single Population | 58.4% | 43.1% | 50.2% |
| Never Married | 43.7% | 27.2% | 33.8% |
| Divorced | 10.8% | 8.7% | 10.8% |
| Widowed | 3.9% | 7.2% | 5.6% |
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| Household Size | 2.58 | 2.59 | 2.60 |
| Households | 3,536 | 5,902 | 124,010,992 |
| Family Households | 2,075 | 3,997 | 80,755,759 |
| Married couple, w/children | 28.5% | 36.9% | 30.5% |
| Married couple, no children | 41.1% | 47.2% | 42.9% |
| Non Family Households | 1,461 | 1,905 | 43,255,233 |
| Single householder, w/children | 16.3% | 5.8% | 15.8% |
| Single householder, no children | 14.1% | 10.1% | 10.8% |