| | Marshfield, WI | Belgrade, MT | United States |
| Population | 18,668 | 10,555 | 329,725,481 |
| Female Population | 52.5% | 52.4% | 50.5% |
| Male Population | 47.5% | 47.6% | 49.5% |
| Median Age | 42.9 | 33.5 | 38.4 |
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| Population - 2010 | 19,099 | 7,492 | 309,327,143 |
| Population - 2000 | 18,800 | 5,728 | 285,036,114 |
| Population - 1990 | 19,291 | 3,411 | 251,960,433 |
| Pop. 2000 to Now | -2.1% | 81.4% | 15.6% |
| Pop. 1990 to Now | -4.6% | 204.6% | 30.8% |
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| Population Density | 1,368.2 | 2,771.8 | 93.4 |
| Land Area | 13.6 | 3.8 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Marshfield, WI | Belgrade, MT | United States |
| Age 0 to 4 | 5.2% | 8.9% | 5.9% |
| Age 5 to 9 | 4.9% | 8.4% | 6.1% |
| Age 10 to 14 | 5.9% | 5.6% | 6.6% |
| Age 15 to 17 | 3.5% | 3.8% | 3.9% |
| Age 18 to 20 | 3.5% | 2.8% | 4.0% |
| Age 21 to 24 | 3.5% | 4.5% | 5.2% |
| Age 25 to 34 | 13.3% | 19.0% | 13.8% |
| Age 35 to 44 | 12.2% | 21.7% | 12.9% |
| Age 45 to 54 | 11.5% | 7.8% | 12.6% |
| Age 55 to 59 | 6.7% | 4.9% | 6.7% |
| Age 60 to 64 | 7.4% | 6.8% | 6.3% |
| Age 65 to 74 | 12.3% | 4.7% | 9.6% |
| Age 75 to 84 | 6.5% | 0.8% | 4.5% |
| Age 85 and over | 3.7% | 0.3% | 1.9% |
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| Race | | | |
| | Marshfield, WI | Belgrade, MT | United States |
| White | 91.5% | 93.3% | 59.4% |
| Black | 1.3% | 0.0% | 12.2% |
| Asian | 2.8% | 0.2% | 5.6% |
| Native American | 0.1% | 1.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.1% | 1.9% | 0.4% |
| Two or More Races | 2.0% | 1.2% | 3.2% |
| Hispanic | 2.3% | 2.2% | 18.4% |
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| Marriage & Family | | | |
| | Marshfield, WI | Belgrade, MT | United States |
| Married Population | 48.5% | 53.8% | 49.8% |
| Currently Married | 47.3% | 53.0% | 48.0% |
| Married but Separated | 1.2% | 0.8% | 1.8% |
| Single Population | 51.5% | 46.2% | 50.2% |
| Never Married | 30.2% | 35.2% | 33.8% |
| Divorced | 14.5% | 10.0% | 10.8% |
| Widowed | 6.8% | 1.0% | 5.6% |
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| Household Size | 2.09 | 2.48 | 2.60 |
| Households | 8,802 | 4,251 | 124,010,992 |
| Family Households | 4,793 | 2,442 | 80,755,759 |
| Married couple, w/children | 21.2% | 37.1% | 30.5% |
| Married couple, no children | 50.7% | 42.2% | 42.9% |
| Non Family Households | 4,009 | 1,809 | 43,255,233 |
| Single householder, w/children | 17.3% | 14.9% | 15.8% |
| Single householder, no children | 10.8% | 5.9% | 10.8% |