| | Gainesville, GA | Decatur, GA | United States |
| Population | 41,730 | 24,334 | 329,725,481 |
| Female Population | 53.4% | 52.6% | 50.5% |
| Male Population | 46.6% | 47.4% | 49.5% |
| Median Age | 32.4 | 38.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 34,066 | 19,700 | 309,327,143 |
| Population - 2000 | 25,578 | 18,147 | 285,036,114 |
| Population - 1990 | 17,885 | 17,336 | 251,960,433 |
| Pop. 2000 to Now | 72.9% | 41.4% | 15.6% |
| Pop. 1990 to Now | 147.2% | 48.0% | 30.8% |
| space4 | | | |
| Population Density | 1,273.3 | 5,485.6 | 93.4 |
| Land Area | 32.8 | 4.4 | 3,531,905.4 |
| Water Area | 1.9 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Gainesville, GA | Decatur, GA | United States |
| Age 0 to 4 | 7.2% | 6.9% | 5.9% |
| Age 5 to 9 | 7.8% | 10.7% | 6.1% |
| Age 10 to 14 | 6.4% | 10.2% | 6.6% |
| Age 15 to 17 | 5.1% | 4.4% | 3.9% |
| Age 18 to 20 | 4.8% | 3.3% | 4.0% |
| Age 21 to 24 | 6.8% | 2.4% | 5.2% |
| Age 25 to 34 | 15.4% | 7.6% | 13.8% |
| Age 35 to 44 | 12.2% | 15.3% | 12.9% |
| Age 45 to 54 | 10.7% | 16.0% | 12.6% |
| Age 55 to 59 | 4.9% | 6.5% | 6.7% |
| Age 60 to 64 | 4.0% | 5.3% | 6.3% |
| Age 65 to 74 | 9.2% | 6.9% | 9.6% |
| Age 75 to 84 | 3.4% | 3.0% | 4.5% |
| Age 85 and over | 2.1% | 1.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Gainesville, GA | Decatur, GA | United States |
| White | 40.2% | 66.9% | 59.4% |
| Black | 16.0% | 15.6% | 12.2% |
| Asian | 2.7% | 3.9% | 5.6% |
| Native American | 0.0% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.8% | 0.0% | 0.4% |
| Two or More Races | 2.2% | 6.5% | 3.2% |
| Hispanic | 38.1% | 6.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Gainesville, GA | Decatur, GA | United States |
| Married Population | 44.6% | 58.3% | 49.8% |
| Currently Married | 42.0% | 56.7% | 48.0% |
| Married but Separated | 2.6% | 1.6% | 1.8% |
| Single Population | 55.4% | 41.7% | 50.2% |
| Never Married | 38.8% | 27.6% | 33.8% |
| Divorced | 11.7% | 9.6% | 10.8% |
| Widowed | 4.8% | 4.6% | 5.6% |
| space5 | | | |
| Household Size | 2.78 | 2.64 | 2.60 |
| Households | 14,619 | 8,906 | 124,010,992 |
| Family Households | 9,307 | 5,849 | 80,755,759 |
| Married couple, w/children | 32.1% | 52.8% | 30.5% |
| Married couple, no children | 31.9% | 31.0% | 42.9% |
| Non Family Households | 5,312 | 3,057 | 43,255,233 |
| Single householder, w/children | 22.8% | 12.1% | 15.8% |
| Single householder, no children | 13.2% | 4.2% | 10.8% |