| | Union, NJ | St. Leo, FL | United States |
| Population | 6,514 | 1,277 | 329,725,481 |
| Female Population | 51.1% | 44.6% | 50.5% |
| Male Population | 48.9% | 55.4% | 49.5% |
| Median Age | 45.3 | 19.4 | 38.4 |
| space3 | | | |
| Population - 2010 | 5,891 | 1,173 | 309,327,143 |
| Population - 2000 | 6,160 | 595 | 285,036,114 |
| Population - 1990 | 5,078 | 1,009 | 251,960,433 |
| Pop. 2000 to Now | -8.3% | 130.6% | 15.6% |
| Pop. 1990 to Now | 11.2% | 36.0% | 30.8% |
| space4 | | | |
| Population Density | 347.7 | 1,086.8 | 93.4 |
| Land Area | 18.7 | 1.2 | 3,531,905.4 |
| Water Area | 1.9 | 0.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Union, NJ | St. Leo, FL | United States |
| Age 0 to 4 | 2.6% | 0.0% | 5.9% |
| Age 5 to 9 | 2.8% | 0.2% | 6.1% |
| Age 10 to 14 | 4.4% | 0.5% | 6.6% |
| Age 15 to 17 | 7.2% | 1.2% | 3.9% |
| Age 18 to 20 | 6.4% | 79.6% | 4.0% |
| Age 21 to 24 | 6.9% | 10.2% | 5.2% |
| Age 25 to 34 | 10.2% | 3.1% | 13.8% |
| Age 35 to 44 | 9.1% | 0.9% | 12.9% |
| Age 45 to 54 | 16.2% | 0.3% | 12.6% |
| Age 55 to 59 | 10.2% | 0.5% | 6.7% |
| Age 60 to 64 | 5.5% | 0.9% | 6.3% |
| Age 65 to 74 | 9.9% | 1.8% | 9.6% |
| Age 75 to 84 | 7.6% | 0.8% | 4.5% |
| Age 85 and over | 1.1% | 0.1% | 1.9% |
| space1 | | | |
| Race | | | |
| | Union, NJ | St. Leo, FL | United States |
| White | 83.1% | 53.7% | 59.4% |
| Black | 9.1% | 27.2% | 12.2% |
| Asian | 2.5% | 1.6% | 5.6% |
| Native American | 0.2% | 2.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.8% | 0.0% | 0.4% |
| Two or More Races | 1.8% | 3.5% | 3.2% |
| Hispanic | 2.5% | 11.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Union, NJ | St. Leo, FL | United States |
| Married Population | 47.6% | 3.4% | 49.8% |
| Currently Married | 47.2% | 3.4% | 48.0% |
| Married but Separated | 0.4% | 0.0% | 1.8% |
| Single Population | 52.4% | 96.6% | 50.2% |
| Never Married | 40.9% | 95.8% | 33.8% |
| Divorced | 7.2% | 0.3% | 10.8% |
| Widowed | 4.3% | 0.5% | 5.6% |
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| Household Size | 2.42 | 2.17 | 2.60 |
| Households | 2,108 | 29 | 124,010,992 |
| Family Households | 1,530 | 18 | 80,755,759 |
| Married couple, w/children | 26.9% | 22.2% | 30.5% |
| Married couple, no children | 60.1% | 72.2% | 42.9% |
| Non Family Households | 578 | 11 | 43,255,233 |
| Single householder, w/children | 5.2% | 0.0% | 15.8% |
| Single householder, no children | 7.8% | 5.6% | 10.8% |