| | Snellville, GA | Decatur, GA | United States |
| Population | 20,475 | 24,334 | 329,725,481 |
| Female Population | 53.1% | 52.6% | 50.5% |
| Male Population | 46.9% | 47.4% | 49.5% |
| Median Age | 39.6 | 38.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 18,317 | 19,700 | 309,327,143 |
| Population - 2000 | 15,351 | 18,147 | 285,036,114 |
| Population - 1990 | 12,084 | 17,336 | 251,960,433 |
| Pop. 2000 to Now | 31.5% | 41.4% | 15.6% |
| Pop. 1990 to Now | 67.0% | 48.0% | 30.8% |
| space4 | | | |
| Population Density | 1,963.8 | 5,485.6 | 93.4 |
| Land Area | 10.4 | 4.4 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Snellville, GA | Decatur, GA | United States |
| Age 0 to 4 | 4.9% | 6.9% | 5.9% |
| Age 5 to 9 | 6.0% | 10.7% | 6.1% |
| Age 10 to 14 | 6.9% | 10.2% | 6.6% |
| Age 15 to 17 | 4.3% | 4.4% | 3.9% |
| Age 18 to 20 | 2.0% | 3.3% | 4.0% |
| Age 21 to 24 | 4.3% | 2.4% | 5.2% |
| Age 25 to 34 | 15.7% | 7.6% | 13.8% |
| Age 35 to 44 | 11.7% | 15.3% | 12.9% |
| Age 45 to 54 | 13.2% | 16.0% | 12.6% |
| Age 55 to 59 | 7.1% | 6.5% | 6.7% |
| Age 60 to 64 | 8.1% | 5.3% | 6.3% |
| Age 65 to 74 | 7.9% | 6.9% | 9.6% |
| Age 75 to 84 | 4.7% | 3.0% | 4.5% |
| Age 85 and over | 3.1% | 1.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Snellville, GA | Decatur, GA | United States |
| White | 37.1% | 66.9% | 59.4% |
| Black | 39.0% | 15.6% | 12.2% |
| Asian | 8.1% | 3.9% | 5.6% |
| Native American | 1.5% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.0% | 0.4% |
| Two or More Races | 3.8% | 6.5% | 3.2% |
| Hispanic | 10.1% | 6.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Snellville, GA | Decatur, GA | United States |
| Married Population | 52.2% | 58.3% | 49.8% |
| Currently Married | 50.9% | 56.7% | 48.0% |
| Married but Separated | 1.3% | 1.6% | 1.8% |
| Single Population | 47.8% | 41.7% | 50.2% |
| Never Married | 33.3% | 27.6% | 33.8% |
| Divorced | 10.0% | 9.6% | 10.8% |
| Widowed | 4.5% | 4.6% | 5.6% |
| space5 | | | |
| Household Size | 3.06 | 2.64 | 2.60 |
| Households | 6,559 | 8,906 | 124,010,992 |
| Family Households | 5,094 | 5,849 | 80,755,759 |
| Married couple, w/children | 30.3% | 52.8% | 30.5% |
| Married couple, no children | 45.4% | 31.0% | 42.9% |
| Non Family Households | 1,465 | 3,057 | 43,255,233 |
| Single householder, w/children | 12.5% | 12.1% | 15.8% |
| Single householder, no children | 11.8% | 4.2% | 10.8% |