| | Clarksville, TN | Madison, AL | United States |
| Population | 163,518 | 55,551 | 329,725,481 |
| Female Population | 49.8% | 50.4% | 50.5% |
| Male Population | 50.2% | 49.6% | 49.5% |
| Median Age | 30 | 38.8 | 38.4 |
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| Population - 2010 | 133,483 | 43,558 | 309,327,143 |
| Population - 2000 | 103,455 | 29,329 | 285,036,114 |
| Population - 1990 | 75,494 | 14,904 | 251,960,433 |
| Pop. 2000 to Now | 55.9% | 79.5% | 15.6% |
| Pop. 1990 to Now | 113.6% | 253.3% | 30.8% |
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| Population Density | 1,668.4 | 1,832.4 | 93.4 |
| Land Area | 98.0 | 30.3 | 3,531,905.4 |
| Water Area | 0.7 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Clarksville, TN | Madison, AL | United States |
| Age 0 to 4 | 8.9% | 5.8% | 5.9% |
| Age 5 to 9 | 7.7% | 7.7% | 6.1% |
| Age 10 to 14 | 7.1% | 8.9% | 6.6% |
| Age 15 to 17 | 3.7% | 6.0% | 3.9% |
| Age 18 to 20 | 4.4% | 2.3% | 4.0% |
| Age 21 to 24 | 7.2% | 2.3% | 5.2% |
| Age 25 to 34 | 20.3% | 11.8% | 13.8% |
| Age 35 to 44 | 13.8% | 15.4% | 12.9% |
| Age 45 to 54 | 9.6% | 14.9% | 12.6% |
| Age 55 to 59 | 4.3% | 6.7% | 6.7% |
| Age 60 to 64 | 4.6% | 6.7% | 6.3% |
| Age 65 to 74 | 5.3% | 6.7% | 9.6% |
| Age 75 to 84 | 2.2% | 3.8% | 4.5% |
| Age 85 and over | 0.8% | 1.0% | 1.9% |
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| Race | | | |
| | Clarksville, TN | Madison, AL | United States |
| White | 56.7% | 69.2% | 59.4% |
| Black | 21.8% | 13.8% | 12.2% |
| Asian | 2.6% | 6.6% | 5.6% |
| Native American | 0.3% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.3% | 0.0% | 0.2% |
| Other | 0.7% | 0.5% | 0.4% |
| Two or More Races | 5.9% | 2.8% | 3.2% |
| Hispanic | 11.7% | 6.6% | 18.4% |
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| Marriage & Family | | | |
| | Clarksville, TN | Madison, AL | United States |
| Married Population | 52.4% | 62.2% | 49.8% |
| Currently Married | 50.3% | 61.4% | 48.0% |
| Married but Separated | 2.1% | 0.9% | 1.8% |
| Single Population | 47.6% | 37.8% | 50.2% |
| Never Married | 30.2% | 24.8% | 33.8% |
| Divorced | 13.6% | 8.0% | 10.8% |
| Widowed | 3.9% | 4.9% | 5.6% |
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| Household Size | 2.69 | 2.59 | 2.60 |
| Households | 59,481 | 21,357 | 124,010,992 |
| Family Households | 41,036 | 15,241 | 80,755,759 |
| Married couple, w/children | 35.3% | 44.7% | 30.5% |
| Married couple, no children | 35.2% | 39.5% | 42.9% |
| Non Family Households | 18,445 | 6,116 | 43,255,233 |
| Single householder, w/children | 20.3% | 12.6% | 15.8% |
| Single householder, no children | 9.3% | 3.2% | 10.8% |