| | Merrick, NY | Key Largo, FL | United States |
| Population | 20,990 | 10,854 | 329,725,481 |
| Female Population | 48.4% | 48.1% | 50.5% |
| Male Population | 51.6% | 51.9% | 49.5% |
| Median Age | 43.3 | 52 | 38.4 |
| space3 | | | |
| Population - 2010 | 21,326 | 11,540 | 309,327,143 |
| Population - 2000 | 22,764 | 11,886 | 285,036,114 |
| Population - 1990 | 23,042 | 11,336 | 251,960,433 |
| Pop. 2000 to Now | -9.4% | -18.4% | 15.6% |
| Pop. 1990 to Now | -10.5% | -14.5% | 30.8% |
| space4 | | | |
| Population Density | 5,275.2 | 900.7 | 93.4 |
| Land Area | 4.0 | 12.1 | 3,531,905.4 |
| Water Area | 1.2 | 3.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Merrick, NY | Key Largo, FL | United States |
| Age 0 to 4 | 5.9% | 3.5% | 5.9% |
| Age 5 to 9 | 6.8% | 3.9% | 6.1% |
| Age 10 to 14 | 5.9% | 5.7% | 6.6% |
| Age 15 to 17 | 4.4% | 1.4% | 3.9% |
| Age 18 to 20 | 2.8% | 1.3% | 4.0% |
| Age 21 to 24 | 3.8% | 2.8% | 5.2% |
| Age 25 to 34 | 8.1% | 8.6% | 13.8% |
| Age 35 to 44 | 14.0% | 13.0% | 12.9% |
| Age 45 to 54 | 14.7% | 15.8% | 12.6% |
| Age 55 to 59 | 7.6% | 8.2% | 6.7% |
| Age 60 to 64 | 8.9% | 8.1% | 6.3% |
| Age 65 to 74 | 10.7% | 17.1% | 9.6% |
| Age 75 to 84 | 4.9% | 6.8% | 4.5% |
| Age 85 and over | 1.4% | 3.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Merrick, NY | Key Largo, FL | United States |
| White | 85.2% | 70.7% | 59.4% |
| Black | 1.0% | 0.2% | 12.2% |
| Asian | 3.3% | 0.6% | 5.6% |
| Native American | 0.2% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.5% | 0.4% |
| Two or More Races | 1.8% | 0.9% | 3.2% |
| Hispanic | 8.2% | 27.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Merrick, NY | Key Largo, FL | United States |
| Married Population | 66.1% | 54.3% | 49.8% |
| Currently Married | 65.2% | 53.8% | 48.0% |
| Married but Separated | 0.9% | 0.4% | 1.8% |
| Single Population | 33.9% | 45.7% | 50.2% |
| Never Married | 23.6% | 21.8% | 33.8% |
| Divorced | 6.4% | 15.7% | 10.8% |
| Widowed | 3.9% | 8.3% | 5.6% |
| space5 | | | |
| Household Size | 2.92 | 2.35 | 2.60 |
| Households | 7,176 | 4,612 | 124,010,992 |
| Family Households | 5,984 | 2,846 | 80,755,759 |
| Married couple, w/children | 39.6% | 19.2% | 30.5% |
| Married couple, no children | 49.5% | 60.8% | 42.9% |
| Non Family Households | 1,192 | 1,766 | 43,255,233 |
| Single householder, w/children | 4.9% | 9.1% | 15.8% |
| Single householder, no children | 6.0% | 11.0% | 10.8% |