| | Valhalla, NY | Stony Brook, NY | United States |
| Population | 3,135 | 12,048 | 329,725,481 |
| Female Population | 47.4% | 46.7% | 50.5% |
| Male Population | 52.6% | 53.4% | 49.5% |
| Median Age | 40.7 | 45.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,083 | 13,658 | 309,327,143 |
| Population - 2000 | 5,379 | 13,727 | 285,036,114 |
| Population - 1990 | 2,791 | 13,726 | 251,960,433 |
| Pop. 2000 to Now | -38.8% | -4.2% | 15.6% |
| Pop. 1990 to Now | 18.0% | -4.2% | 30.8% |
| space4 | | | |
| Population Density | 3,809.2 | 2,075.1 | 93.4 |
| Land Area | 0.8 | 5.8 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Valhalla, NY | Stony Brook, NY | United States |
| Age 0 to 4 | 8.1% | 5.2% | 5.9% |
| Age 5 to 9 | 4.3% | 5.1% | 6.1% |
| Age 10 to 14 | 6.3% | 6.7% | 6.6% |
| Age 15 to 17 | 2.6% | 4.4% | 3.9% |
| Age 18 to 20 | 3.2% | 2.9% | 4.0% |
| Age 21 to 24 | 3.6% | 6.6% | 5.2% |
| Age 25 to 34 | 16.0% | 10.0% | 13.8% |
| Age 35 to 44 | 10.1% | 8.3% | 12.9% |
| Age 45 to 54 | 9.4% | 15.8% | 12.6% |
| Age 55 to 59 | 8.3% | 7.2% | 6.7% |
| Age 60 to 64 | 8.4% | 5.8% | 6.3% |
| Age 65 to 74 | 9.4% | 13.2% | 9.6% |
| Age 75 to 84 | 4.5% | 6.1% | 4.5% |
| Age 85 and over | 5.7% | 2.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Valhalla, NY | Stony Brook, NY | United States |
| White | 74.3% | 79.3% | 59.4% |
| Black | 7.4% | 1.2% | 12.2% |
| Asian | 2.2% | 12.4% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 1.0% | 0.9% | 3.2% |
| Hispanic | 15.2% | 6.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Valhalla, NY | Stony Brook, NY | United States |
| Married Population | 58.3% | 62.5% | 49.8% |
| Currently Married | 55.5% | 60.5% | 48.0% |
| Married but Separated | 2.9% | 1.9% | 1.8% |
| Single Population | 41.7% | 37.5% | 50.2% |
| Never Married | 29.2% | 26.4% | 33.8% |
| Divorced | 5.6% | 6.3% | 10.8% |
| Widowed | 6.9% | 4.9% | 5.6% |
| space5 | | | |
| Household Size | 2.92 | 2.77 | 2.60 |
| Households | 1,075 | 4,335 | 124,010,992 |
| Family Households | 773 | 3,276 | 80,755,759 |
| Married couple, w/children | 28.2% | 38.7% | 30.5% |
| Married couple, no children | 47.1% | 48.4% | 42.9% |
| Non Family Households | 302 | 1,059 | 43,255,233 |
| Single householder, w/children | 16.0% | 5.4% | 15.8% |
| Single householder, no children | 8.7% | 7.5% | 10.8% |