| | Gallatin, TN | Charleston, SC | United States |
| Population | 43,306 | 147,928 | 329,725,481 |
| Female Population | 50.1% | 52.6% | 50.5% |
| Male Population | 49.9% | 47.5% | 49.5% |
| Median Age | 38.2 | 35.5 | 38.4 |
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| Population - 2010 | 30,514 | 120,760 | 309,327,143 |
| Population - 2000 | 23,230 | 96,650 | 285,036,114 |
| Population - 1990 | 18,794 | 80,414 | 251,960,433 |
| Pop. 2000 to Now | 90.9% | 44.6% | 15.6% |
| Pop. 1990 to Now | 135.9% | 73.7% | 30.8% |
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| Population Density | 1,363.0 | 1,337.8 | 93.4 |
| Land Area | 31.8 | 110.6 | 3,531,905.4 |
| Water Area | 0.6 | 20.3 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Gallatin, TN | Charleston, SC | United States |
| Age 0 to 4 | 5.8% | 5.8% | 5.9% |
| Age 5 to 9 | 8.0% | 4.9% | 6.1% |
| Age 10 to 14 | 6.0% | 3.7% | 6.6% |
| Age 15 to 17 | 2.9% | 2.5% | 3.9% |
| Age 18 to 20 | 3.7% | 5.2% | 4.0% |
| Age 21 to 24 | 4.4% | 6.9% | 5.2% |
| Age 25 to 34 | 14.5% | 20.2% | 13.8% |
| Age 35 to 44 | 13.1% | 12.9% | 12.9% |
| Age 45 to 54 | 13.6% | 10.7% | 12.6% |
| Age 55 to 59 | 6.5% | 6.3% | 6.7% |
| Age 60 to 64 | 5.3% | 5.7% | 6.3% |
| Age 65 to 74 | 9.0% | 9.2% | 9.6% |
| Age 75 to 84 | 5.5% | 4.0% | 4.5% |
| Age 85 and over | 1.7% | 2.0% | 1.9% |
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| Race | | | |
| | Gallatin, TN | Charleston, SC | United States |
| White | 69.9% | 71.7% | 59.4% |
| Black | 13.9% | 19.6% | 12.2% |
| Asian | 2.8% | 1.8% | 5.6% |
| Native American | 0.2% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.2% | 0.2% |
| Other | 0.2% | 0.4% | 0.4% |
| Two or More Races | 4.6% | 2.0% | 3.2% |
| Hispanic | 8.3% | 4.2% | 18.4% |
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| Marriage & Family | | | |
| | Gallatin, TN | Charleston, SC | United States |
| Married Population | 52.0% | 44.9% | 49.8% |
| Currently Married | 51.2% | 43.3% | 48.0% |
| Married but Separated | 0.8% | 1.6% | 1.8% |
| Single Population | 48.0% | 55.1% | 50.2% |
| Never Married | 29.0% | 40.3% | 33.8% |
| Divorced | 13.0% | 9.8% | 10.8% |
| Widowed | 6.0% | 5.1% | 5.6% |
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| Household Size | 2.47 | 2.23 | 2.60 |
| Households | 17,127 | 63,760 | 124,010,992 |
| Family Households | 11,622 | 33,199 | 80,755,759 |
| Married couple, w/children | 26.9% | 29.0% | 30.5% |
| Married couple, no children | 45.1% | 49.2% | 42.9% |
| Non Family Households | 5,505 | 30,561 | 43,255,233 |
| Single householder, w/children | 17.7% | 11.5% | 15.8% |
| Single householder, no children | 10.2% | 10.4% | 10.8% |