| | Knoxville, TN | Decatur, AL | United States |
| Population | 189,339 | 57,303 | 329,725,481 |
| Female Population | 51.7% | 50.7% | 50.5% |
| Male Population | 48.3% | 49.3% | 49.5% |
| Median Age | 33.5 | 40.6 | 38.4 |
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| Population - 2010 | 178,269 | 55,810 | 309,327,143 |
| Population - 2000 | 173,890 | 53,929 | 285,036,114 |
| Population - 1990 | 165,121 | 48,761 | 251,960,433 |
| Pop. 2000 to Now | 9.4% | 0.8% | 15.6% |
| Pop. 1990 to Now | 15.2% | 11.5% | 30.8% |
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| Population Density | 1,918.1 | 1,058.9 | 93.4 |
| Land Area | 98.7 | 54.1 | 3,531,905.4 |
| Water Area | 5.5 | 6.6 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Knoxville, TN | Decatur, AL | United States |
| Age 0 to 4 | 5.3% | 6.5% | 5.9% |
| Age 5 to 9 | 5.5% | 6.1% | 6.1% |
| Age 10 to 14 | 4.9% | 6.1% | 6.6% |
| Age 15 to 17 | 3.2% | 4.4% | 3.9% |
| Age 18 to 20 | 7.1% | 2.6% | 4.0% |
| Age 21 to 24 | 9.9% | 5.0% | 5.2% |
| Age 25 to 34 | 15.9% | 12.1% | 13.8% |
| Age 35 to 44 | 11.9% | 12.4% | 12.9% |
| Age 45 to 54 | 11.1% | 12.4% | 12.6% |
| Age 55 to 59 | 6.0% | 6.2% | 6.7% |
| Age 60 to 64 | 5.2% | 7.2% | 6.3% |
| Age 65 to 74 | 8.3% | 10.9% | 9.6% |
| Age 75 to 84 | 3.9% | 5.9% | 4.5% |
| Age 85 and over | 1.7% | 2.2% | 1.9% |
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| Race | | | |
| | Knoxville, TN | Decatur, AL | United States |
| White | 72.1% | 59.9% | 59.4% |
| Black | 16.3% | 22.6% | 12.2% |
| Asian | 1.7% | 0.4% | 5.6% |
| Native American | 0.1% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.4% | 0.4% |
| Two or More Races | 3.8% | 2.5% | 3.2% |
| Hispanic | 5.7% | 14.1% | 18.4% |
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| Marriage & Family | | | |
| | Knoxville, TN | Decatur, AL | United States |
| Married Population | 36.7% | 49.9% | 49.8% |
| Currently Married | 34.5% | 47.2% | 48.0% |
| Married but Separated | 2.2% | 2.6% | 1.8% |
| Single Population | 63.3% | 50.1% | 50.2% |
| Never Married | 43.4% | 28.3% | 33.8% |
| Divorced | 13.8% | 13.3% | 10.8% |
| Widowed | 6.1% | 8.5% | 5.6% |
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| Household Size | 2.19 | 2.37 | 2.60 |
| Households | 82,586 | 23,797 | 124,010,992 |
| Family Households | 39,549 | 14,199 | 80,755,759 |
| Married couple, w/children | 25.1% | 25.6% | 30.5% |
| Married couple, no children | 38.6% | 46.0% | 42.9% |
| Non Family Households | 43,037 | 9,598 | 43,255,233 |
| Single householder, w/children | 23.9% | 17.9% | 15.8% |
| Single householder, no children | 12.5% | 10.6% | 10.8% |