| | Yacolt, WA | Monmouth, OR | United States |
| Population | 1,482 | 10,735 | 329,725,481 |
| Female Population | 47.4% | 53.8% | 50.5% |
| Male Population | 52.6% | 46.3% | 49.5% |
| Median Age | 28.1 | 25 | 38.4 |
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| Population - 2010 | 1,583 | 9,550 | 309,327,143 |
| Population - 2000 | 1,055 | 7,741 | 285,036,114 |
| Population - 1990 | 600 | 6,288 | 251,960,433 |
| Pop. 2000 to Now | 70.8% | 37.1% | 15.6% |
| Pop. 1990 to Now | 200.3% | 68.8% | 30.8% |
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| Population Density | 2,679.9 | 4,949.3 | 93.4 |
| Land Area | 0.6 | 2.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Yacolt, WA | Monmouth, OR | United States |
| Age 0 to 4 | 13.0% | 3.2% | 5.9% |
| Age 5 to 9 | 6.4% | 9.7% | 6.1% |
| Age 10 to 14 | 4.7% | 5.9% | 6.6% |
| Age 15 to 17 | 2.1% | 4.7% | 3.9% |
| Age 18 to 20 | 1.6% | 15.6% | 4.0% |
| Age 21 to 24 | 11.1% | 11.0% | 5.2% |
| Age 25 to 34 | 21.8% | 14.8% | 13.8% |
| Age 35 to 44 | 7.8% | 8.2% | 12.9% |
| Age 45 to 54 | 11.2% | 10.2% | 12.6% |
| Age 55 to 59 | 3.8% | 3.2% | 6.7% |
| Age 60 to 64 | 5.3% | 5.5% | 6.3% |
| Age 65 to 74 | 6.3% | 3.8% | 9.6% |
| Age 75 to 84 | 4.7% | 3.4% | 4.5% |
| Age 85 and over | 0.3% | 0.7% | 1.9% |
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| Race | | | |
| | Yacolt, WA | Monmouth, OR | United States |
| White | 95.4% | 70.0% | 59.4% |
| Black | 1.8% | 2.0% | 12.2% |
| Asian | 0.1% | 2.8% | 5.6% |
| Native American | 0.0% | 1.5% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.8% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 1.3% | 3.6% | 3.2% |
| Hispanic | 1.5% | 19.4% | 18.4% |
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| Marriage & Family | | | |
| | Yacolt, WA | Monmouth, OR | United States |
| Married Population | 64.2% | 38.6% | 49.8% |
| Currently Married | 63.5% | 36.3% | 48.0% |
| Married but Separated | 0.7% | 2.2% | 1.8% |
| Single Population | 35.8% | 61.4% | 50.2% |
| Never Married | 24.7% | 48.8% | 33.8% |
| Divorced | 9.8% | 11.1% | 10.8% |
| Widowed | 1.3% | 1.5% | 5.6% |
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| Household Size | 2.95 | 2.89 | 2.60 |
| Households | 502 | 3,346 | 124,010,992 |
| Family Households | 370 | 2,051 | 80,755,759 |
| Married couple, w/children | 43.5% | 41.8% | 30.5% |
| Married couple, no children | 41.4% | 32.7% | 42.9% |
| Non Family Households | 132 | 1,295 | 43,255,233 |
| Single householder, w/children | 8.9% | 13.3% | 15.8% |
| Single householder, no children | 6.2% | 12.1% | 10.8% |