| | Three Rivers, MI | Allegan, MI | United States |
| Population | 7,946 | 5,165 | 329,725,481 |
| Female Population | 52.3% | 49.5% | 50.5% |
| Male Population | 47.8% | 50.6% | 49.5% |
| Median Age | 33 | 31.8 | 38.4 |
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| Population - 2010 | 7,811 | 4,996 | 309,327,143 |
| Population - 2000 | 7,328 | 4,838 | 285,036,114 |
| Population - 1990 | 7,413 | 4,547 | 251,960,433 |
| Pop. 2000 to Now | 3.7% | 3.7% | 15.6% |
| Pop. 1990 to Now | 2.5% | 10.3% | 30.8% |
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| Population Density | 1,473.4 | 1,343.0 | 93.4 |
| Land Area | 5.4 | 3.8 | 3,531,905.4 |
| Water Area | 0.3 | 0.4 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Three Rivers, MI | Allegan, MI | United States |
| Age 0 to 4 | 8.4% | 4.7% | 5.9% |
| Age 5 to 9 | 8.4% | 8.0% | 6.1% |
| Age 10 to 14 | 7.1% | 7.4% | 6.6% |
| Age 15 to 17 | 3.1% | 3.3% | 3.9% |
| Age 18 to 20 | 3.9% | 4.0% | 4.0% |
| Age 21 to 24 | 5.8% | 14.4% | 5.2% |
| Age 25 to 34 | 16.8% | 14.2% | 13.8% |
| Age 35 to 44 | 12.7% | 8.8% | 12.9% |
| Age 45 to 54 | 7.5% | 8.1% | 12.6% |
| Age 55 to 59 | 7.1% | 7.8% | 6.7% |
| Age 60 to 64 | 6.0% | 5.3% | 6.3% |
| Age 65 to 74 | 7.9% | 7.3% | 9.6% |
| Age 75 to 84 | 3.5% | 4.8% | 4.5% |
| Age 85 and over | 1.8% | 1.9% | 1.9% |
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| Race | | | |
| | Three Rivers, MI | Allegan, MI | United States |
| White | 74.5% | 84.1% | 59.4% |
| Black | 10.7% | 5.3% | 12.2% |
| Asian | 1.6% | 1.5% | 5.6% |
| Native American | 0.1% | 0.7% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.4% | 0.4% |
| Two or More Races | 5.6% | 3.0% | 3.2% |
| Hispanic | 7.5% | 5.0% | 18.4% |
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| Marriage & Family | | | |
| | Three Rivers, MI | Allegan, MI | United States |
| Married Population | 33.8% | 46.1% | 49.8% |
| Currently Married | 32.8% | 44.2% | 48.0% |
| Married but Separated | 1.0% | 1.9% | 1.8% |
| Single Population | 66.2% | 53.9% | 50.2% |
| Never Married | 36.0% | 36.5% | 33.8% |
| Divorced | 21.7% | 11.3% | 10.8% |
| Widowed | 8.5% | 6.1% | 5.6% |
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| Household Size | 2.39 | 2.54 | 2.60 |
| Households | 3,258 | 1,939 | 124,010,992 |
| Family Households | 1,943 | 1,264 | 80,755,759 |
| Married couple, w/children | 26.8% | 31.6% | 30.5% |
| Married couple, no children | 19.9% | 37.9% | 42.9% |
| Non Family Households | 1,315 | 675 | 43,255,233 |
| Single householder, w/children | 27.9% | 17.3% | 15.8% |
| Single householder, no children | 25.3% | 13.2% | 10.8% |