| | Plymouth, WI | Davenport, IA | United States |
| Population | 8,883 | 101,725 | 329,725,481 |
| Female Population | 53.4% | 50.4% | 50.5% |
| Male Population | 46.6% | 49.6% | 49.5% |
| Median Age | 43.7 | 37.8 | 38.4 |
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| Population - 2010 | 8,458 | 99,683 | 309,327,143 |
| Population - 2000 | 7,781 | 98,359 | 285,036,114 |
| Population - 1990 | 6,769 | 95,333 | 251,960,433 |
| Pop. 2000 to Now | 12.3% | 3.5% | 15.6% |
| Pop. 1990 to Now | 29.1% | 6.8% | 30.8% |
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| Population Density | 1,703.0 | 1,601.0 | 93.4 |
| Land Area | 5.2 | 63.5 | 3,531,905.4 |
| Water Area | 0.1 | 2.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Plymouth, WI | Davenport, IA | United States |
| Age 0 to 4 | 5.8% | 6.2% | 5.9% |
| Age 5 to 9 | 7.1% | 5.7% | 6.1% |
| Age 10 to 14 | 5.7% | 6.0% | 6.6% |
| Age 15 to 17 | 2.8% | 3.8% | 3.9% |
| Age 18 to 20 | 2.6% | 4.3% | 4.0% |
| Age 21 to 24 | 4.4% | 5.7% | 5.2% |
| Age 25 to 34 | 12.9% | 14.5% | 13.8% |
| Age 35 to 44 | 10.5% | 12.8% | 12.9% |
| Age 45 to 54 | 12.7% | 11.9% | 12.6% |
| Age 55 to 59 | 6.5% | 7.0% | 6.7% |
| Age 60 to 64 | 7.5% | 6.5% | 6.3% |
| Age 65 to 74 | 13.4% | 9.4% | 9.6% |
| Age 75 to 84 | 5.2% | 4.1% | 4.5% |
| Age 85 and over | 3.0% | 2.2% | 1.9% |
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| Race | | | |
| | Plymouth, WI | Davenport, IA | United States |
| White | 93.1% | 72.9% | 59.4% |
| Black | 2.2% | 10.7% | 12.2% |
| Asian | 0.7% | 2.2% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 1.8% | 4.7% | 3.2% |
| Hispanic | 2.2% | 8.9% | 18.4% |
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| Marriage & Family | | | |
| | Plymouth, WI | Davenport, IA | United States |
| Married Population | 51.1% | 44.8% | 49.8% |
| Currently Married | 50.7% | 43.5% | 48.0% |
| Married but Separated | 0.3% | 1.3% | 1.8% |
| Single Population | 48.9% | 55.2% | 50.2% |
| Never Married | 26.8% | 36.9% | 33.8% |
| Divorced | 12.6% | 12.7% | 10.8% |
| Widowed | 9.5% | 5.6% | 5.6% |
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| Household Size | 2.16 | 2.36 | 2.60 |
| Households | 4,082 | 41,882 | 124,010,992 |
| Family Households | 2,318 | 23,778 | 80,755,759 |
| Married couple, w/children | 24.7% | 25.3% | 30.5% |
| Married couple, no children | 53.8% | 45.5% | 42.9% |
| Non Family Households | 1,764 | 18,104 | 43,255,233 |
| Single householder, w/children | 16.3% | 19.2% | 15.8% |
| Single householder, no children | 5.3% | 10.0% | 10.8% |