| | Needham, MA | Belmont, MA | United States |
| Population | 31,808 | 27,056 | 329,725,481 |
| Female Population | 53.1% | 52.8% | 50.5% |
| Male Population | 46.9% | 47.2% | 49.5% |
| Median Age | 43.4 | 41.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 29,170 | 24,700 | 309,327,143 |
| Population - 2000 | 28,911 | 24,194 | 285,036,114 |
| Population - 1990 | 27,557 | 24,720 | 251,960,433 |
| Pop. 2000 to Now | 9.1% | 6.9% | 15.6% |
| Pop. 1990 to Now | 14.4% | 4.7% | 30.8% |
| space4 | | | |
| Population Density | 2,589.0 | 5,817.2 | 93.4 |
| Land Area | 12.3 | 4.7 | 3,531,905.4 |
| Water Area | 0.4 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Needham, MA | Belmont, MA | United States |
| Age 0 to 4 | 4.9% | 6.3% | 5.9% |
| Age 5 to 9 | 8.5% | 7.3% | 6.1% |
| Age 10 to 14 | 9.0% | 6.1% | 6.6% |
| Age 15 to 17 | 5.3% | 5.0% | 3.9% |
| Age 18 to 20 | 3.0% | 2.3% | 4.0% |
| Age 21 to 24 | 3.3% | 2.9% | 5.2% |
| Age 25 to 34 | 4.9% | 9.8% | 13.8% |
| Age 35 to 44 | 13.8% | 15.3% | 12.9% |
| Age 45 to 54 | 14.2% | 15.1% | 12.6% |
| Age 55 to 59 | 7.9% | 7.0% | 6.7% |
| Age 60 to 64 | 6.5% | 5.6% | 6.3% |
| Age 65 to 74 | 9.7% | 10.0% | 9.6% |
| Age 75 to 84 | 4.9% | 5.0% | 4.5% |
| Age 85 and over | 4.0% | 2.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Needham, MA | Belmont, MA | United States |
| White | 81.6% | 72.5% | 59.4% |
| Black | 2.3% | 1.2% | 12.2% |
| Asian | 9.3% | 18.2% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 2.6% | 3.9% | 3.2% |
| Hispanic | 4.2% | 4.2% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Needham, MA | Belmont, MA | United States |
| Married Population | 67.3% | 64.4% | 49.8% |
| Currently Married | 66.5% | 63.6% | 48.0% |
| Married but Separated | 0.8% | 0.9% | 1.8% |
| Single Population | 32.7% | 35.6% | 50.2% |
| Never Married | 22.0% | 24.7% | 33.8% |
| Divorced | 6.0% | 5.6% | 10.8% |
| Widowed | 4.7% | 5.3% | 5.6% |
| space5 | | | |
| Household Size | 2.76 | 2.58 | 2.60 |
| Households | 11,260 | 10,393 | 124,010,992 |
| Family Households | 9,005 | 7,556 | 80,755,759 |
| Married couple, w/children | 46.5% | 45.1% | 30.5% |
| Married couple, no children | 42.2% | 41.5% | 42.9% |
| Non Family Households | 2,255 | 2,837 | 43,255,233 |
| Single householder, w/children | 6.2% | 7.7% | 15.8% |
| Single householder, no children | 5.1% | 5.8% | 10.8% |