| | Old Greenwich, CT | Larchmont, NY | United States |
| Population | 6,929 | 6,532 | 329,725,481 |
| Female Population | 49.5% | 50.3% | 50.5% |
| Male Population | 50.5% | 49.8% | 49.5% |
| Median Age | 40.6 | 34.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 6,568 | 5,941 | 309,327,143 |
| Population - 2000 | 6,496 | 6,485 | 285,036,114 |
| Population - 1990 | 5,789 | 6,181 | 251,960,433 |
| Pop. 2000 to Now | 5.3% | -5.7% | 15.6% |
| Pop. 1990 to Now | 18.1% | -1.1% | 30.8% |
| space4 | | | |
| Population Density | 3,473.2 | 6,065.0 | 93.4 |
| Land Area | 2.0 | 1.1 | 3,531,905.4 |
| Water Area | 1.5 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Old Greenwich, CT | Larchmont, NY | United States |
| Age 0 to 4 | 7.7% | 8.4% | 5.9% |
| Age 5 to 9 | 13.0% | 12.0% | 6.1% |
| Age 10 to 14 | 10.0% | 9.8% | 6.6% |
| Age 15 to 17 | 5.6% | 3.7% | 3.9% |
| Age 18 to 20 | 1.3% | 1.7% | 4.0% |
| Age 21 to 24 | 2.0% | 1.2% | 5.2% |
| Age 25 to 34 | 1.8% | 13.2% | 13.8% |
| Age 35 to 44 | 17.7% | 18.7% | 12.9% |
| Age 45 to 54 | 15.6% | 11.2% | 12.6% |
| Age 55 to 59 | 6.8% | 5.7% | 6.7% |
| Age 60 to 64 | 4.5% | 6.8% | 6.3% |
| Age 65 to 74 | 8.5% | 2.9% | 9.6% |
| Age 75 to 84 | 3.6% | 3.3% | 4.5% |
| Age 85 and over | 2.0% | 1.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Old Greenwich, CT | Larchmont, NY | United States |
| White | 79.7% | 80.5% | 59.4% |
| Black | 0.5% | 0.3% | 12.2% |
| Asian | 6.8% | 5.0% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.6% | 0.2% | 0.4% |
| Two or More Races | 3.9% | 4.7% | 3.2% |
| Hispanic | 8.4% | 9.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Old Greenwich, CT | Larchmont, NY | United States |
| Married Population | 70.5% | 62.9% | 49.8% |
| Currently Married | 69.8% | 62.3% | 48.0% |
| Married but Separated | 0.6% | 0.6% | 1.8% |
| Single Population | 29.5% | 37.1% | 50.2% |
| Never Married | 20.1% | 28.5% | 33.8% |
| Divorced | 5.9% | 6.1% | 10.8% |
| Widowed | 3.5% | 2.5% | 5.6% |
| space5 | | | |
| Household Size | 3.01 | 3.10 | 2.60 |
| Households | 2,297 | 2,102 | 124,010,992 |
| Family Households | 1,765 | 1,623 | 80,755,759 |
| Married couple, w/children | 58.2% | 55.1% | 30.5% |
| Married couple, no children | 32.5% | 35.3% | 42.9% |
| Non Family Households | 532 | 479 | 43,255,233 |
| Single householder, w/children | 4.9% | 5.6% | 15.8% |
| Single householder, no children | 4.5% | 4.0% | 10.8% |