| | Brooklyn, NY | San Mateo, CA | United States |
| Population | 2,712,360 | 105,087 | 329,725,481 |
| Female Population | 52.4% | 50.4% | 50.5% |
| Male Population | 47.6% | 49.6% | 49.5% |
| Median Age | 35.7 | 37.7 | 38.4 |
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| Population - 2010 | 2,509,954 | 97,256 | 309,327,143 |
| Population - 2000 | 2,465,326 | 92,482 | 285,036,114 |
| Population - 1990 | 2,300,664 | 85,486 | 251,960,433 |
| Pop. 2000 to Now | 3.0% | 10.7% | 15.6% |
| Pop. 1990 to Now | 10.4% | 19.8% | 30.8% |
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| Population Density | 38,301.5 | 8,632.8 | 93.4 |
| Land Area | 70.8 | 12.2 | 3,531,905.4 |
| Water Area | 26.1 | 3.7 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Brooklyn, NY | San Mateo, CA | United States |
| Age 0 to 4 | 7.1% | 6.7% | 5.9% |
| Age 5 to 9 | 6.2% | 5.6% | 6.1% |
| Age 10 to 14 | 6.2% | 5.7% | 6.6% |
| Age 15 to 17 | 3.5% | 2.7% | 3.9% |
| Age 18 to 20 | 2.9% | 2.6% | 4.0% |
| Age 21 to 24 | 4.9% | 4.1% | 5.2% |
| Age 25 to 34 | 18.0% | 17.5% | 13.8% |
| Age 35 to 44 | 14.2% | 15.4% | 12.9% |
| Age 45 to 54 | 11.7% | 12.7% | 12.6% |
| Age 55 to 59 | 5.8% | 5.8% | 6.7% |
| Age 60 to 64 | 5.4% | 5.7% | 6.3% |
| Age 65 to 74 | 8.2% | 8.0% | 9.6% |
| Age 75 to 84 | 4.1% | 4.8% | 4.5% |
| Age 85 and over | 1.8% | 2.8% | 1.9% |
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| Race | | | |
| | Brooklyn, NY | San Mateo, CA | United States |
| White | 36.7% | 40.9% | 59.4% |
| Black | 28.6% | 1.9% | 12.2% |
| Asian | 11.7% | 25.2% | 5.6% |
| Native American | 0.1% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 1.7% | 0.2% |
| Other | 0.7% | 0.6% | 0.4% |
| Two or More Races | 3.3% | 5.5% | 3.2% |
| Hispanic | 18.8% | 24.1% | 18.4% |
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| Marriage & Family | | | |
| | Brooklyn, NY | San Mateo, CA | United States |
| Married Population | 43.1% | 52.6% | 49.8% |
| Currently Married | 40.3% | 51.3% | 48.0% |
| Married but Separated | 2.8% | 1.2% | 1.8% |
| Single Population | 56.9% | 47.4% | 50.2% |
| Never Married | 44.3% | 33.0% | 33.8% |
| Divorced | 7.4% | 8.9% | 10.8% |
| Widowed | 5.2% | 5.6% | 5.6% |
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| Household Size | 2.71 | 2.58 | 2.60 |
| Households | 985,108 | 40,233 | 124,010,992 |
| Family Households | 599,788 | 25,420 | 80,755,759 |
| Married couple, w/children | 28.9% | 35.1% | 30.5% |
| Married couple, no children | 33.2% | 43.3% | 42.9% |
| Non Family Households | 385,320 | 14,813 | 43,255,233 |
| Single householder, w/children | 18.8% | 10.4% | 15.8% |
| Single householder, no children | 19.1% | 11.3% | 10.8% |