| | Middleton, WI | Gallatin, TN | United States |
| Population | 21,634 | 43,306 | 329,725,481 |
| Female Population | 51.5% | 50.1% | 50.5% |
| Male Population | 48.5% | 49.9% | 49.5% |
| Median Age | 38.2 | 38.2 | 38.4 |
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| Population - 2010 | 17,625 | 30,514 | 309,327,143 |
| Population - 2000 | 15,770 | 23,230 | 285,036,114 |
| Population - 1990 | 13,289 | 18,794 | 251,960,433 |
| Pop. 2000 to Now | 28.1% | 90.9% | 15.6% |
| Pop. 1990 to Now | 52.0% | 135.9% | 30.8% |
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| Population Density | 2,423.4 | 1,363.0 | 93.4 |
| Land Area | 8.9 | 31.8 | 3,531,905.4 |
| Water Area | 0.1 | 0.6 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Middleton, WI | Gallatin, TN | United States |
| Age 0 to 4 | 5.2% | 5.8% | 5.9% |
| Age 5 to 9 | 4.8% | 8.0% | 6.1% |
| Age 10 to 14 | 6.7% | 6.0% | 6.6% |
| Age 15 to 17 | 4.1% | 2.9% | 3.9% |
| Age 18 to 20 | 2.1% | 3.7% | 4.0% |
| Age 21 to 24 | 3.8% | 4.4% | 5.2% |
| Age 25 to 34 | 17.9% | 14.5% | 13.8% |
| Age 35 to 44 | 14.0% | 13.1% | 12.9% |
| Age 45 to 54 | 13.7% | 13.6% | 12.6% |
| Age 55 to 59 | 6.9% | 6.5% | 6.7% |
| Age 60 to 64 | 5.1% | 5.3% | 6.3% |
| Age 65 to 74 | 9.2% | 9.0% | 9.6% |
| Age 75 to 84 | 5.0% | 5.5% | 4.5% |
| Age 85 and over | 1.5% | 1.7% | 1.9% |
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| Race | | | |
| | Middleton, WI | Gallatin, TN | United States |
| White | 79.4% | 69.9% | 59.4% |
| Black | 3.5% | 13.9% | 12.2% |
| Asian | 6.5% | 2.8% | 5.6% |
| Native American | 0.2% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 1.4% | 0.2% | 0.4% |
| Two or More Races | 3.3% | 4.6% | 3.2% |
| Hispanic | 5.7% | 8.3% | 18.4% |
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| Marriage & Family | | | |
| | Middleton, WI | Gallatin, TN | United States |
| Married Population | 54.0% | 52.0% | 49.8% |
| Currently Married | 52.3% | 51.2% | 48.0% |
| Married but Separated | 1.7% | 0.8% | 1.8% |
| Single Population | 46.0% | 48.0% | 50.2% |
| Never Married | 31.9% | 29.0% | 33.8% |
| Divorced | 10.9% | 13.0% | 10.8% |
| Widowed | 3.3% | 6.0% | 5.6% |
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| Household Size | 2.14 | 2.47 | 2.60 |
| Households | 10,052 | 17,127 | 124,010,992 |
| Family Households | 5,709 | 11,622 | 80,755,759 |
| Married couple, w/children | 30.8% | 26.9% | 30.5% |
| Married couple, no children | 46.7% | 45.1% | 42.9% |
| Non Family Households | 4,343 | 5,505 | 43,255,233 |
| Single householder, w/children | 17.4% | 17.7% | 15.8% |
| Single householder, no children | 5.0% | 10.2% | 10.8% |