| | Fennimore, WI | Fairfax, VA | United States |
| Population | 2,750 | 23,980 | 329,725,481 |
| Female Population | 51.3% | 51.2% | 50.5% |
| Male Population | 48.7% | 48.9% | 49.5% |
| Median Age | 35.4 | 37.7 | 38.4 |
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| Population - 2010 | 2,523 | 22,616 | 309,327,143 |
| Population - 2000 | 2,387 | 21,498 | 285,036,114 |
| Population - 1990 | 2,378 | 19,622 | 251,960,433 |
| Pop. 2000 to Now | 3.4% | 9.0% | 15.6% |
| Pop. 1990 to Now | 3.8% | 19.4% | 30.8% |
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| Population Density | 1,596.1 | 3,843.0 | 93.4 |
| Land Area | 1.7 | 6.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Fennimore, WI | Fairfax, VA | United States |
| Age 0 to 4 | 7.3% | 7.4% | 5.9% |
| Age 5 to 9 | 4.9% | 5.5% | 6.1% |
| Age 10 to 14 | 7.6% | 6.0% | 6.6% |
| Age 15 to 17 | 4.2% | 3.5% | 3.9% |
| Age 18 to 20 | 6.9% | 3.4% | 4.0% |
| Age 21 to 24 | 4.4% | 6.0% | 5.2% |
| Age 25 to 34 | 14.3% | 13.1% | 13.8% |
| Age 35 to 44 | 13.6% | 13.8% | 12.9% |
| Age 45 to 54 | 10.7% | 13.2% | 12.6% |
| Age 55 to 59 | 3.9% | 7.9% | 6.7% |
| Age 60 to 64 | 7.1% | 5.4% | 6.3% |
| Age 65 to 74 | 7.3% | 8.6% | 9.6% |
| Age 75 to 84 | 5.7% | 4.2% | 4.5% |
| Age 85 and over | 2.2% | 2.0% | 1.9% |
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| Race | | | |
| | Fennimore, WI | Fairfax, VA | United States |
| White | 97.1% | 54.6% | 59.4% |
| Black | 0.0% | 5.4% | 12.2% |
| Asian | 0.4% | 18.4% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 0.7% | 3.7% | 3.2% |
| Hispanic | 1.8% | 17.7% | 18.4% |
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| Marriage & Family | | | |
| | Fennimore, WI | Fairfax, VA | United States |
| Married Population | 54.5% | 56.3% | 49.8% |
| Currently Married | 54.0% | 55.1% | 48.0% |
| Married but Separated | 0.5% | 1.2% | 1.8% |
| Single Population | 45.5% | 43.7% | 50.2% |
| Never Married | 31.7% | 31.9% | 33.8% |
| Divorced | 8.2% | 7.3% | 10.8% |
| Widowed | 5.6% | 4.5% | 5.6% |
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| Household Size | 2.44 | 2.58 | 2.60 |
| Households | 1,106 | 9,090 | 124,010,992 |
| Family Households | 675 | 5,849 | 80,755,759 |
| Married couple, w/children | 42.8% | 41.2% | 30.5% |
| Married couple, no children | 39.4% | 42.7% | 42.9% |
| Non Family Households | 431 | 3,241 | 43,255,233 |
| Single householder, w/children | 14.7% | 6.1% | 15.8% |
| Single householder, no children | 3.1% | 10.0% | 10.8% |