| | Brentwood, NY | Commack, NY | United States |
| Population | 66,035 | 36,252 | 329,725,481 |
| Female Population | 50.0% | 50.4% | 50.5% |
| Male Population | 50.0% | 49.6% | 49.5% |
| Median Age | 35.3 | 45 | 38.4 |
| space3 | | | |
| Population - 2010 | 54,818 | 36,153 | 309,327,143 |
| Population - 2000 | 53,917 | 36,367 | 285,036,114 |
| Population - 1990 | 45,218 | 36,124 | 251,960,433 |
| Pop. 2000 to Now | 15.7% | 0.9% | 15.6% |
| Pop. 1990 to Now | 37.9% | 1.5% | 30.8% |
| space4 | | | |
| Population Density | 6,021.3 | 3,031.1 | 93.4 |
| Land Area | 11.0 | 12.0 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Brentwood, NY | Commack, NY | United States |
| Age 0 to 4 | 6.1% | 5.2% | 5.9% |
| Age 5 to 9 | 6.5% | 4.9% | 6.1% |
| Age 10 to 14 | 6.6% | 6.9% | 6.6% |
| Age 15 to 17 | 4.0% | 4.6% | 3.9% |
| Age 18 to 20 | 3.0% | 3.8% | 4.0% |
| Age 21 to 24 | 6.4% | 5.6% | 5.2% |
| Age 25 to 34 | 16.7% | 9.8% | 13.8% |
| Age 35 to 44 | 14.5% | 9.2% | 12.9% |
| Age 45 to 54 | 14.5% | 17.0% | 12.6% |
| Age 55 to 59 | 6.0% | 8.7% | 6.7% |
| Age 60 to 64 | 6.2% | 7.2% | 6.3% |
| Age 65 to 74 | 5.8% | 8.8% | 9.6% |
| Age 75 to 84 | 2.4% | 5.0% | 4.5% |
| Age 85 and over | 1.4% | 3.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Brentwood, NY | Commack, NY | United States |
| White | 10.3% | 84.2% | 59.4% |
| Black | 12.1% | 1.1% | 12.2% |
| Asian | 1.8% | 5.0% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.2% | 0.0% | 0.2% |
| Other | 1.0% | 0.1% | 0.4% |
| Two or More Races | 1.0% | 1.7% | 3.2% |
| Hispanic | 73.5% | 7.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Brentwood, NY | Commack, NY | United States |
| Married Population | 43.2% | 60.4% | 49.8% |
| Currently Married | 40.6% | 60.2% | 48.0% |
| Married but Separated | 2.6% | 0.2% | 1.8% |
| Single Population | 56.8% | 39.6% | 50.2% |
| Never Married | 45.3% | 27.9% | 33.8% |
| Divorced | 7.5% | 5.8% | 10.8% |
| Widowed | 4.0% | 5.9% | 5.6% |
| space5 | | | |
| Household Size | 4.39 | 3.09 | 2.60 |
| Households | 14,762 | 11,583 | 124,010,992 |
| Family Households | 12,332 | 9,672 | 80,755,759 |
| Married couple, w/children | 32.3% | 37.4% | 30.5% |
| Married couple, no children | 30.8% | 50.2% | 42.9% |
| Non Family Households | 2,430 | 1,911 | 43,255,233 |
| Single householder, w/children | 19.1% | 3.2% | 15.8% |
| Single householder, no children | 17.8% | 9.2% | 10.8% |