| | Mount Juliet, TN | Decatur, TN | United States |
| Population | 38,059 | 1,841 | 329,725,481 |
| Female Population | 49.6% | 53.5% | 50.5% |
| Male Population | 50.4% | 46.6% | 49.5% |
| Median Age | 38.4 | 40.2 | 38.4 |
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| Population - 2010 | 24,988 | 1,645 | 309,327,143 |
| Population - 2000 | 12,366 | 1,395 | 285,036,114 |
| Population - 1990 | 5,389 | 1,361 | 251,960,433 |
| Pop. 2000 to Now | 211.6% | 19.2% | 15.6% |
| Pop. 1990 to Now | 614.9% | 22.2% | 30.8% |
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| Population Density | 1,534.5 | 485.0 | 93.4 |
| Land Area | 24.8 | 3.8 | 3,531,905.4 |
| Water Area | 0.3 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Mount Juliet, TN | Decatur, TN | United States |
| Age 0 to 4 | 6.4% | 7.9% | 5.9% |
| Age 5 to 9 | 8.3% | 6.1% | 6.1% |
| Age 10 to 14 | 7.8% | 4.0% | 6.6% |
| Age 15 to 17 | 4.5% | 4.6% | 3.9% |
| Age 18 to 20 | 2.6% | 4.1% | 4.0% |
| Age 21 to 24 | 4.3% | 7.3% | 5.2% |
| Age 25 to 34 | 10.7% | 10.6% | 13.8% |
| Age 35 to 44 | 16.2% | 14.4% | 12.9% |
| Age 45 to 54 | 13.2% | 10.0% | 12.6% |
| Age 55 to 59 | 5.8% | 6.6% | 6.7% |
| Age 60 to 64 | 6.1% | 3.6% | 6.3% |
| Age 65 to 74 | 9.5% | 10.8% | 9.6% |
| Age 75 to 84 | 3.7% | 8.3% | 4.5% |
| Age 85 and over | 0.7% | 1.6% | 1.9% |
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| Race | | | |
| | Mount Juliet, TN | Decatur, TN | United States |
| White | 79.0% | 90.4% | 59.4% |
| Black | 7.0% | 3.7% | 12.2% |
| Asian | 3.9% | 0.0% | 5.6% |
| Native American | 0.1% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.0% | 0.2% |
| Other | 1.8% | 0.0% | 0.4% |
| Two or More Races | 2.1% | 4.0% | 3.2% |
| Hispanic | 6.0% | 1.7% | 18.4% |
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| Marriage & Family | | | |
| | Mount Juliet, TN | Decatur, TN | United States |
| Married Population | 60.9% | 47.7% | 49.8% |
| Currently Married | 60.3% | 41.9% | 48.0% |
| Married but Separated | 0.6% | 5.8% | 1.8% |
| Single Population | 39.1% | 52.3% | 50.2% |
| Never Married | 23.3% | 30.6% | 33.8% |
| Divorced | 11.3% | 11.1% | 10.8% |
| Widowed | 4.5% | 10.5% | 5.6% |
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| Household Size | 2.78 | 2.40 | 2.60 |
| Households | 13,672 | 724 | 124,010,992 |
| Family Households | 10,446 | 446 | 80,755,759 |
| Married couple, w/children | 40.2% | 29.4% | 30.5% |
| Married couple, no children | 41.9% | 32.3% | 42.9% |
| Non Family Households | 3,226 | 278 | 43,255,233 |
| Single householder, w/children | 13.9% | 26.0% | 15.8% |
| Single householder, no children | 4.0% | 12.3% | 10.8% |