| | Jefferson, WI | Beloit, WI | United States |
| Population | 7,821 | 36,567 | 329,725,481 |
| Female Population | 52.7% | 51.7% | 50.5% |
| Male Population | 47.4% | 48.3% | 49.5% |
| Median Age | 45.8 | 33.5 | 38.4 |
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| Population - 2010 | 7,985 | 36,982 | 309,327,143 |
| Population - 2000 | 7,338 | 35,775 | 285,036,114 |
| Population - 1990 | 6,078 | 35,573 | 251,960,433 |
| Pop. 2000 to Now | 9.5% | 2.4% | 15.6% |
| Pop. 1990 to Now | 32.2% | 3.0% | 30.8% |
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| Population Density | 1,342.0 | 2,111.9 | 93.4 |
| Land Area | 5.8 | 17.3 | 3,531,905.4 |
| Water Area | 0.2 | 0.3 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Jefferson, WI | Beloit, WI | United States |
| Age 0 to 4 | 3.8% | 8.0% | 5.9% |
| Age 5 to 9 | 5.0% | 7.7% | 6.1% |
| Age 10 to 14 | 5.3% | 6.8% | 6.6% |
| Age 15 to 17 | 3.6% | 3.3% | 3.9% |
| Age 18 to 20 | 2.8% | 6.3% | 4.0% |
| Age 21 to 24 | 2.5% | 6.0% | 5.2% |
| Age 25 to 34 | 13.1% | 13.8% | 13.8% |
| Age 35 to 44 | 12.9% | 11.6% | 12.9% |
| Age 45 to 54 | 15.8% | 10.7% | 12.6% |
| Age 55 to 59 | 8.4% | 6.6% | 6.7% |
| Age 60 to 64 | 9.4% | 5.8% | 6.3% |
| Age 65 to 74 | 11.3% | 8.5% | 9.6% |
| Age 75 to 84 | 4.3% | 3.5% | 4.5% |
| Age 85 and over | 1.8% | 1.4% | 1.9% |
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| Race | | | |
| | Jefferson, WI | Beloit, WI | United States |
| White | 84.0% | 57.2% | 59.4% |
| Black | 2.0% | 14.1% | 12.2% |
| Asian | 0.2% | 1.5% | 5.6% |
| Native American | 0.1% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.2% | 0.4% |
| Two or More Races | 2.7% | 5.6% | 3.2% |
| Hispanic | 10.7% | 21.1% | 18.4% |
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| Marriage & Family | | | |
| | Jefferson, WI | Beloit, WI | United States |
| Married Population | 49.4% | 39.9% | 49.8% |
| Currently Married | 47.4% | 37.8% | 48.0% |
| Married but Separated | 1.9% | 2.2% | 1.8% |
| Single Population | 50.6% | 60.1% | 50.2% |
| Never Married | 25.8% | 42.3% | 33.8% |
| Divorced | 18.7% | 12.0% | 10.8% |
| Widowed | 6.2% | 5.8% | 5.6% |
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| Household Size | 2.16 | 2.55 | 2.60 |
| Households | 3,430 | 13,677 | 124,010,992 |
| Family Households | 1,967 | 7,919 | 80,755,759 |
| Married couple, w/children | 26.1% | 28.3% | 30.5% |
| Married couple, no children | 52.2% | 35.8% | 42.9% |
| Non Family Households | 1,463 | 5,758 | 43,255,233 |
| Single householder, w/children | 12.9% | 23.9% | 15.8% |
| Single householder, no children | 8.9% | 12.0% | 10.8% |