| | St. Charles, MN | Arlington, WA | United States |
| Population | 3,962 | 19,832 | 329,725,481 |
| Female Population | 48.7% | 50.9% | 50.5% |
| Male Population | 51.3% | 49.1% | 49.5% |
| Median Age | 40.8 | 39.2 | 38.4 |
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| Population - 2010 | 3,740 | 17,987 | 309,327,143 |
| Population - 2000 | 3,295 | 11,713 | 285,036,114 |
| Population - 1990 | 2,642 | 4,037 | 251,960,433 |
| Pop. 2000 to Now | 14.4% | 79.9% | 15.6% |
| Pop. 1990 to Now | 42.6% | 421.9% | 30.8% |
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| Population Density | 1,070.8 | 2,023.5 | 93.4 |
| Land Area | 3.7 | 9.8 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Charles, MN | Arlington, WA | United States |
| Age 0 to 4 | 8.4% | 5.9% | 5.9% |
| Age 5 to 9 | 5.4% | 6.0% | 6.1% |
| Age 10 to 14 | 6.3% | 7.7% | 6.6% |
| Age 15 to 17 | 2.4% | 3.9% | 3.9% |
| Age 18 to 20 | 1.9% | 3.2% | 4.0% |
| Age 21 to 24 | 3.5% | 4.5% | 5.2% |
| Age 25 to 34 | 14.3% | 11.4% | 13.8% |
| Age 35 to 44 | 16.3% | 16.7% | 12.9% |
| Age 45 to 54 | 11.9% | 14.7% | 12.6% |
| Age 55 to 59 | 9.3% | 5.7% | 6.7% |
| Age 60 to 64 | 5.4% | 7.7% | 6.3% |
| Age 65 to 74 | 8.1% | 7.2% | 9.6% |
| Age 75 to 84 | 4.9% | 3.5% | 4.5% |
| Age 85 and over | 1.8% | 2.1% | 1.9% |
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| Race | | | |
| | St. Charles, MN | Arlington, WA | United States |
| White | 89.7% | 71.4% | 59.4% |
| Black | 0.0% | 1.6% | 12.2% |
| Asian | 5.6% | 5.6% | 5.6% |
| Native American | 0.0% | 0.7% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.5% | 0.2% |
| Other | 0.7% | 0.4% | 0.4% |
| Two or More Races | 1.2% | 5.9% | 3.2% |
| Hispanic | 2.9% | 14.0% | 18.4% |
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| Marriage & Family | | | |
| | St. Charles, MN | Arlington, WA | United States |
| Married Population | 57.2% | 56.8% | 49.8% |
| Currently Married | 57.2% | 54.8% | 48.0% |
| Married but Separated | 0.0% | 2.0% | 1.8% |
| Single Population | 42.8% | 43.2% | 50.2% |
| Never Married | 22.9% | 24.5% | 33.8% |
| Divorced | 14.1% | 12.6% | 10.8% |
| Widowed | 5.8% | 6.2% | 5.6% |
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| Household Size | 2.43 | 2.64 | 2.60 |
| Households | 1,619 | 7,493 | 124,010,992 |
| Family Households | 1,055 | 5,168 | 80,755,759 |
| Married couple, w/children | 33.0% | 38.7% | 30.5% |
| Married couple, no children | 50.7% | 42.0% | 42.9% |
| Non Family Households | 564 | 2,325 | 43,255,233 |
| Single householder, w/children | 8.2% | 11.1% | 15.8% |
| Single householder, no children | 8.1% | 8.2% | 10.8% |