| | Mendham borough, NJ | Long Valley, NJ | United States |
| Population | 4,976 | 2,108 | 329,725,481 |
| Female Population | 55.1% | 48.1% | 50.5% |
| Male Population | 44.9% | 51.9% | 49.5% |
| Median Age | 47.7 | 44.9 | 38.4 |
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| Population - 2010 | 4,995 | 1,885 | 309,327,143 |
| Population - 2000 | 5,097 | 1,818 | 285,036,114 |
| Population - 1990 | 4,890 | 1,744 | 251,960,433 |
| Pop. 2000 to Now | -5.1% | 10.6% | 15.6% |
| Pop. 1990 to Now | -1.1% | 15.3% | 30.8% |
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| Population Density | 839.0 | 461.7 | 93.4 |
| Land Area | 5.9 | 4.6 | 3,531,905.4 |
| Water Area | 0.1 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Mendham borough, NJ | Long Valley, NJ | United States |
| Age 0 to 4 | 4.4% | 7.6% | 5.9% |
| Age 5 to 9 | 6.3% | 3.2% | 6.1% |
| Age 10 to 14 | 6.6% | 3.7% | 6.6% |
| Age 15 to 17 | 6.4% | 14.4% | 3.9% |
| Age 18 to 20 | 2.5% | 1.9% | 4.0% |
| Age 21 to 24 | 4.4% | 6.9% | 5.2% |
| Age 25 to 34 | 6.8% | 7.4% | 13.8% |
| Age 35 to 44 | 9.3% | 5.0% | 12.9% |
| Age 45 to 54 | 18.3% | 13.6% | 12.6% |
| Age 55 to 59 | 7.8% | 9.3% | 6.7% |
| Age 60 to 64 | 6.9% | 5.0% | 6.3% |
| Age 65 to 74 | 10.3% | 15.9% | 9.6% |
| Age 75 to 84 | 5.4% | 6.1% | 4.5% |
| Age 85 and over | 4.6% | 0.0% | 1.9% |
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| Race | | | |
| | Mendham borough, NJ | Long Valley, NJ | United States |
| White | 87.6% | 70.5% | 59.4% |
| Black | 0.9% | 0.0% | 12.2% |
| Asian | 4.2% | 3.7% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 4.1% | 4.6% | 3.2% |
| Hispanic | 3.2% | 21.1% | 18.4% |
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| Marriage & Family | | | |
| | Mendham borough, NJ | Long Valley, NJ | United States |
| Married Population | 63.4% | 55.5% | 49.8% |
| Currently Married | 63.2% | 55.5% | 48.0% |
| Married but Separated | 0.1% | 0.0% | 1.8% |
| Single Population | 36.6% | 44.5% | 50.2% |
| Never Married | 24.0% | 31.0% | 33.8% |
| Divorced | 8.6% | 9.6% | 10.8% |
| Widowed | 4.0% | 3.9% | 5.6% |
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| Household Size | 2.68 | 2.80 | 2.60 |
| Households | 1,753 | 748 | 124,010,992 |
| Family Households | 1,405 | 628 | 80,755,759 |
| Married couple, w/children | 37.8% | 31.1% | 30.5% |
| Married couple, no children | 51.2% | 48.4% | 42.9% |
| Non Family Households | 348 | 120 | 43,255,233 |
| Single householder, w/children | 6.0% | 14.3% | 15.8% |
| Single householder, no children | 5.0% | 6.2% | 10.8% |