| | Monmouth, OR | Cincinnati, OH | United States |
| Population | 10,735 | 308,664 | 329,725,481 |
| Female Population | 53.8% | 51.6% | 50.5% |
| Male Population | 46.3% | 48.4% | 49.5% |
| Median Age | 25 | 32.7 | 38.4 |
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| Population - 2010 | 9,550 | 297,061 | 309,327,143 |
| Population - 2000 | 7,741 | 331,285 | 285,036,114 |
| Population - 1990 | 6,288 | 364,040 | 251,960,433 |
| Pop. 2000 to Now | 37.1% | -8.1% | 15.6% |
| Pop. 1990 to Now | 68.8% | -16.3% | 30.8% |
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| Population Density | 4,949.3 | 3,961.6 | 93.4 |
| Land Area | 2.2 | 77.9 | 3,531,905.4 |
| Water Area | 0.1 | 1.6 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Monmouth, OR | Cincinnati, OH | United States |
| Age 0 to 4 | 3.2% | 6.9% | 5.9% |
| Age 5 to 9 | 9.7% | 5.4% | 6.1% |
| Age 10 to 14 | 5.9% | 5.9% | 6.6% |
| Age 15 to 17 | 4.7% | 3.3% | 3.9% |
| Age 18 to 20 | 15.6% | 6.4% | 4.0% |
| Age 21 to 24 | 11.0% | 7.2% | 5.2% |
| Age 25 to 34 | 14.8% | 18.8% | 13.8% |
| Age 35 to 44 | 8.2% | 12.0% | 12.9% |
| Age 45 to 54 | 10.2% | 10.5% | 12.6% |
| Age 55 to 59 | 3.2% | 6.0% | 6.7% |
| Age 60 to 64 | 5.5% | 5.6% | 6.3% |
| Age 65 to 74 | 3.8% | 7.5% | 9.6% |
| Age 75 to 84 | 3.4% | 3.1% | 4.5% |
| Age 85 and over | 0.7% | 1.6% | 1.9% |
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| Race | | | |
| | Monmouth, OR | Cincinnati, OH | United States |
| White | 70.0% | 48.6% | 59.4% |
| Black | 2.0% | 40.0% | 12.2% |
| Asian | 2.8% | 2.4% | 5.6% |
| Native American | 1.5% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.8% | 0.0% | 0.2% |
| Other | 0.0% | 0.4% | 0.4% |
| Two or More Races | 3.6% | 4.1% | 3.2% |
| Hispanic | 19.4% | 4.4% | 18.4% |
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| Marriage & Family | | | |
| | Monmouth, OR | Cincinnati, OH | United States |
| Married Population | 38.6% | 31.3% | 49.8% |
| Currently Married | 36.3% | 29.1% | 48.0% |
| Married but Separated | 2.2% | 2.2% | 1.8% |
| Single Population | 61.4% | 68.7% | 50.2% |
| Never Married | 48.8% | 52.6% | 33.8% |
| Divorced | 11.1% | 11.7% | 10.8% |
| Widowed | 1.5% | 4.5% | 5.6% |
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| Household Size | 2.89 | 2.11 | 2.60 |
| Households | 3,346 | 139,791 | 124,010,992 |
| Family Households | 2,051 | 62,652 | 80,755,759 |
| Married couple, w/children | 41.8% | 20.5% | 30.5% |
| Married couple, no children | 32.7% | 33.5% | 42.9% |
| Non Family Households | 1,295 | 77,139 | 43,255,233 |
| Single householder, w/children | 13.3% | 31.0% | 15.8% |
| Single householder, no children | 12.1% | 15.0% | 10.8% |