| | Harvey, LA | Gretna, LA | United States |
| Population | 20,942 | 17,836 | 329,725,481 |
| Female Population | 50.3% | 49.2% | 50.5% |
| Male Population | 49.7% | 50.8% | 49.5% |
| Median Age | 37.8 | 40.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 19,918 | 17,741 | 309,327,143 |
| Population - 2000 | 22,226 | 17,423 | 285,036,114 |
| Population - 1990 | 21,222 | 17,208 | 251,960,433 |
| Pop. 2000 to Now | -9.3% | 1.1% | 15.6% |
| Pop. 1990 to Now | -5.0% | 2.4% | 30.8% |
| space4 | | | |
| Population Density | 3,228.3 | 4,447.9 | 93.4 |
| Land Area | 6.5 | 4.0 | 3,531,905.4 |
| Water Area | 0.5 | 0.5 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Harvey, LA | Gretna, LA | United States |
| Age 0 to 4 | 6.9% | 4.7% | 5.9% |
| Age 5 to 9 | 6.4% | 6.6% | 6.1% |
| Age 10 to 14 | 7.4% | 4.6% | 6.6% |
| Age 15 to 17 | 4.9% | 3.0% | 3.9% |
| Age 18 to 20 | 2.5% | 3.2% | 4.0% |
| Age 21 to 24 | 4.4% | 4.7% | 5.2% |
| Age 25 to 34 | 14.2% | 14.9% | 13.8% |
| Age 35 to 44 | 12.9% | 15.7% | 12.9% |
| Age 45 to 54 | 14.0% | 12.2% | 12.6% |
| Age 55 to 59 | 6.2% | 8.3% | 6.7% |
| Age 60 to 64 | 6.4% | 6.3% | 6.3% |
| Age 65 to 74 | 8.8% | 9.1% | 9.6% |
| Age 75 to 84 | 4.1% | 4.8% | 4.5% |
| Age 85 and over | 1.1% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Harvey, LA | Gretna, LA | United States |
| White | 31.1% | 44.6% | 59.4% |
| Black | 48.1% | 31.1% | 12.2% |
| Asian | 7.1% | 2.5% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.1% | 0.0% | 0.4% |
| Two or More Races | 1.3% | 2.4% | 3.2% |
| Hispanic | 12.2% | 19.2% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Harvey, LA | Gretna, LA | United States |
| Married Population | 41.4% | 35.8% | 49.8% |
| Currently Married | 37.5% | 32.4% | 48.0% |
| Married but Separated | 4.0% | 3.3% | 1.8% |
| Single Population | 58.6% | 64.2% | 50.2% |
| Never Married | 37.9% | 41.3% | 33.8% |
| Divorced | 14.4% | 15.2% | 10.8% |
| Widowed | 6.2% | 7.7% | 5.6% |
| space5 | | | |
| Household Size | 2.55 | 2.13 | 2.60 |
| Households | 8,133 | 7,824 | 124,010,992 |
| Family Households | 4,801 | 4,003 | 80,755,759 |
| Married couple, w/children | 24.1% | 22.1% | 30.5% |
| Married couple, no children | 33.2% | 31.2% | 42.9% |
| Non Family Households | 3,332 | 3,821 | 43,255,233 |
| Single householder, w/children | 26.5% | 30.1% | 15.8% |
| Single householder, no children | 16.1% | 16.6% | 10.8% |