| | Wisconsin Rapids, WI | Spencer, WI | United States |
| Population | 18,711 | 1,555 | 329,725,481 |
| Female Population | 53.9% | 47.1% | 50.5% |
| Male Population | 46.2% | 52.9% | 49.5% |
| Median Age | 38.6 | 35.3 | 38.4 |
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| Population - 2010 | 18,395 | 1,923 | 309,327,143 |
| Population - 2000 | 18,435 | 1,932 | 285,036,114 |
| Population - 1990 | 18,245 | 1,757 | 251,960,433 |
| Pop. 2000 to Now | -4.8% | -3.5% | 15.6% |
| Pop. 1990 to Now | -3.8% | 6.2% | 30.8% |
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| Population Density | 1,350.8 | 792.6 | 93.4 |
| Land Area | 13.9 | 2.0 | 3,531,905.4 |
| Water Area | 0.9 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Wisconsin Rapids, WI | Spencer, WI | United States |
| Age 0 to 4 | 5.3% | 6.6% | 5.9% |
| Age 5 to 9 | 6.4% | 4.5% | 6.1% |
| Age 10 to 14 | 7.7% | 9.3% | 6.6% |
| Age 15 to 17 | 3.7% | 3.9% | 3.9% |
| Age 18 to 20 | 3.6% | 1.6% | 4.0% |
| Age 21 to 24 | 5.6% | 4.7% | 5.2% |
| Age 25 to 34 | 12.7% | 18.1% | 13.8% |
| Age 35 to 44 | 11.6% | 13.1% | 12.9% |
| Age 45 to 54 | 11.6% | 12.3% | 12.6% |
| Age 55 to 59 | 7.3% | 4.2% | 6.7% |
| Age 60 to 64 | 4.9% | 3.7% | 6.3% |
| Age 65 to 74 | 9.5% | 11.5% | 9.6% |
| Age 75 to 84 | 5.2% | 4.7% | 4.5% |
| Age 85 and over | 4.9% | 1.7% | 1.9% |
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| Race | | | |
| | Wisconsin Rapids, WI | Spencer, WI | United States |
| White | 85.5% | 98.3% | 59.4% |
| Black | 1.0% | 0.0% | 12.2% |
| Asian | 4.2% | 0.0% | 5.6% |
| Native American | 0.2% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.0% | 0.4% |
| Two or More Races | 3.0% | 0.5% | 3.2% |
| Hispanic | 5.9% | 1.0% | 18.4% |
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| Marriage & Family | | | |
| | Wisconsin Rapids, WI | Spencer, WI | United States |
| Married Population | 40.5% | 53.5% | 49.8% |
| Currently Married | 39.3% | 53.5% | 48.0% |
| Married but Separated | 1.1% | 0.0% | 1.8% |
| Single Population | 59.5% | 46.5% | 50.2% |
| Never Married | 34.3% | 25.9% | 33.8% |
| Divorced | 16.6% | 16.0% | 10.8% |
| Widowed | 8.7% | 4.6% | 5.6% |
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| Household Size | 2.17 | 2.22 | 2.60 |
| Households | 8,409 | 701 | 124,010,992 |
| Family Households | 4,514 | 479 | 80,755,759 |
| Married couple, w/children | 25.4% | 25.3% | 30.5% |
| Married couple, no children | 38.1% | 45.9% | 42.9% |
| Non Family Households | 3,895 | 222 | 43,255,233 |
| Single householder, w/children | 22.7% | 18.4% | 15.8% |
| Single householder, no children | 13.8% | 10.4% | 10.8% |