| | Old Westbury, NY | Brookville, NY | United States |
| Population | 4,567 | 2,937 | 329,725,481 |
| Female Population | 53.6% | 50.9% | 50.5% |
| Male Population | 46.4% | 49.1% | 49.5% |
| Median Age | 27.4 | 23.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 4,702 | 3,483 | 309,327,143 |
| Population - 2000 | 4,228 | 2,126 | 285,036,114 |
| Population - 1990 | 3,897 | 3,716 | 251,960,433 |
| Pop. 2000 to Now | -2.9% | 69.0% | 15.6% |
| Pop. 1990 to Now | 5.3% | -3.3% | 30.8% |
| space4 | | | |
| Population Density | 532.5 | 744.1 | 93.4 |
| Land Area | 8.6 | 3.9 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Old Westbury, NY | Brookville, NY | United States |
| Age 0 to 4 | 1.0% | 3.2% | 5.9% |
| Age 5 to 9 | 3.5% | 4.6% | 6.1% |
| Age 10 to 14 | 4.4% | 3.7% | 6.6% |
| Age 15 to 17 | 4.2% | 4.8% | 3.9% |
| Age 18 to 20 | 24.0% | 25.2% | 4.0% |
| Age 21 to 24 | 11.6% | 10.5% | 5.2% |
| Age 25 to 34 | 5.9% | 4.5% | 13.8% |
| Age 35 to 44 | 6.6% | 8.2% | 12.9% |
| Age 45 to 54 | 10.8% | 14.3% | 12.6% |
| Age 55 to 59 | 5.6% | 8.3% | 6.7% |
| Age 60 to 64 | 7.4% | 3.4% | 6.3% |
| Age 65 to 74 | 8.9% | 6.2% | 9.6% |
| Age 75 to 84 | 3.5% | 3.0% | 4.5% |
| Age 85 and over | 2.5% | 0.1% | 1.9% |
| space1 | | | |
| Race | | | |
| | Old Westbury, NY | Brookville, NY | United States |
| White | 65.5% | 63.0% | 59.4% |
| Black | 7.4% | 4.8% | 12.2% |
| Asian | 13.0% | 16.2% | 5.6% |
| Native American | 0.0% | 0.9% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 1.1% | 0.0% | 0.4% |
| Two or More Races | 5.8% | 3.9% | 3.2% |
| Hispanic | 7.3% | 11.2% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Old Westbury, NY | Brookville, NY | United States |
| Married Population | 41.3% | 46.9% | 49.8% |
| Currently Married | 41.0% | 46.7% | 48.0% |
| Married but Separated | 0.3% | 0.2% | 1.8% |
| Single Population | 58.7% | 53.1% | 50.2% |
| Never Married | 54.0% | 49.1% | 33.8% |
| Divorced | 1.8% | 1.5% | 10.8% |
| Widowed | 2.8% | 2.5% | 5.6% |
| space5 | | | |
| Household Size | 3.04 | 2.66 | 2.60 |
| Households | 1,075 | 733 | 124,010,992 |
| Family Households | 845 | 691 | 80,755,759 |
| Married couple, w/children | 30.8% | 58.2% | 30.5% |
| Married couple, no children | 61.4% | 37.9% | 42.9% |
| Non Family Households | 230 | 42 | 43,255,233 |
| Single householder, w/children | 1.9% | 2.8% | 15.8% |
| Single householder, no children | 5.9% | 1.2% | 10.8% |