| | Cottage Grove, MN | Helena, MT | United States |
| Population | 38,582 | 32,060 | 329,725,481 |
| Female Population | 50.1% | 51.9% | 50.5% |
| Male Population | 49.9% | 48.1% | 49.5% |
| Median Age | 36.3 | 39.9 | 38.4 |
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| Population - 2010 | 34,715 | 28,909 | 309,327,143 |
| Population - 2000 | 30,582 | 25,780 | 285,036,114 |
| Population - 1990 | 22,935 | 24,569 | 251,960,433 |
| Pop. 2000 to Now | 24.8% | 30.9% | 15.6% |
| Pop. 1990 to Now | 66.4% | 37.3% | 30.8% |
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| Population Density | 1,146.9 | 1,919.2 | 93.4 |
| Land Area | 33.6 | 16.7 | 3,531,905.4 |
| Water Area | 3.9 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Cottage Grove, MN | Helena, MT | United States |
| Age 0 to 4 | 6.4% | 4.8% | 5.9% |
| Age 5 to 9 | 7.5% | 5.2% | 6.1% |
| Age 10 to 14 | 8.3% | 5.9% | 6.6% |
| Age 15 to 17 | 4.7% | 3.3% | 3.9% |
| Age 18 to 20 | 3.5% | 4.3% | 4.0% |
| Age 21 to 24 | 4.2% | 6.0% | 5.2% |
| Age 25 to 34 | 12.2% | 12.6% | 13.8% |
| Age 35 to 44 | 17.2% | 13.5% | 12.9% |
| Age 45 to 54 | 13.0% | 10.9% | 12.6% |
| Age 55 to 59 | 6.5% | 6.3% | 6.7% |
| Age 60 to 64 | 4.6% | 6.6% | 6.3% |
| Age 65 to 74 | 6.9% | 11.5% | 9.6% |
| Age 75 to 84 | 3.6% | 6.5% | 4.5% |
| Age 85 and over | 1.3% | 2.5% | 1.9% |
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| Race | | | |
| | Cottage Grove, MN | Helena, MT | United States |
| White | 80.7% | 87.9% | 59.4% |
| Black | 4.9% | 0.6% | 12.2% |
| Asian | 6.7% | 0.8% | 5.6% |
| Native American | 0.0% | 1.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.2% | 0.0% | 0.2% |
| Other | 0.3% | 0.2% | 0.4% |
| Two or More Races | 3.0% | 4.3% | 3.2% |
| Hispanic | 4.3% | 5.0% | 18.4% |
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| Marriage & Family | | | |
| | Cottage Grove, MN | Helena, MT | United States |
| Married Population | 59.3% | 42.2% | 49.8% |
| Currently Married | 58.9% | 41.4% | 48.0% |
| Married but Separated | 0.4% | 0.9% | 1.8% |
| Single Population | 40.7% | 57.8% | 50.2% |
| Never Married | 30.0% | 32.4% | 33.8% |
| Divorced | 7.3% | 18.4% | 10.8% |
| Widowed | 3.5% | 6.9% | 5.6% |
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| Household Size | 3.00 | 2.03 | 2.60 |
| Households | 12,850 | 15,032 | 124,010,992 |
| Family Households | 10,172 | 7,138 | 80,755,759 |
| Married couple, w/children | 40.7% | 29.4% | 30.5% |
| Married couple, no children | 42.4% | 45.9% | 42.9% |
| Non Family Households | 2,678 | 7,894 | 43,255,233 |
| Single householder, w/children | 10.9% | 17.7% | 15.8% |
| Single householder, no children | 6.0% | 7.1% | 10.8% |