| | Monmouth, OR | Dallas, OR | United States |
| Population | 10,735 | 16,663 | 329,725,481 |
| Female Population | 53.8% | 52.8% | 50.5% |
| Male Population | 46.3% | 47.2% | 49.5% |
| Median Age | 25 | 42.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 9,550 | 14,618 | 309,327,143 |
| Population - 2000 | 7,741 | 12,459 | 285,036,114 |
| Population - 1990 | 6,288 | 9,422 | 251,960,433 |
| Pop. 2000 to Now | 37.1% | 39.1% | 15.6% |
| Pop. 1990 to Now | 68.8% | 83.9% | 30.8% |
| space4 | | | |
| Population Density | 4,949.3 | 3,393.0 | 93.4 |
| Land Area | 2.2 | 4.9 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Monmouth, OR | Dallas, OR | United States |
| Age 0 to 4 | 3.2% | 6.3% | 5.9% |
| Age 5 to 9 | 9.7% | 4.0% | 6.1% |
| Age 10 to 14 | 5.9% | 5.5% | 6.6% |
| Age 15 to 17 | 4.7% | 3.2% | 3.9% |
| Age 18 to 20 | 15.6% | 5.0% | 4.0% |
| Age 21 to 24 | 11.0% | 8.2% | 5.2% |
| Age 25 to 34 | 14.8% | 11.7% | 13.8% |
| Age 35 to 44 | 8.2% | 9.4% | 12.9% |
| Age 45 to 54 | 10.2% | 11.0% | 12.6% |
| Age 55 to 59 | 3.2% | 5.4% | 6.7% |
| Age 60 to 64 | 5.5% | 6.7% | 6.3% |
| Age 65 to 74 | 3.8% | 14.0% | 9.6% |
| Age 75 to 84 | 3.4% | 6.3% | 4.5% |
| Age 85 and over | 0.7% | 3.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Monmouth, OR | Dallas, OR | United States |
| White | 70.0% | 87.2% | 59.4% |
| Black | 2.0% | 0.9% | 12.2% |
| Asian | 2.8% | 0.2% | 5.6% |
| Native American | 1.5% | 1.5% | 0.6% |
| Hawaiian, Pacific Islander | 0.8% | 0.0% | 0.2% |
| Other | 0.0% | 1.4% | 0.4% |
| Two or More Races | 3.6% | 3.3% | 3.2% |
| Hispanic | 19.4% | 5.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Monmouth, OR | Dallas, OR | United States |
| Married Population | 38.6% | 52.2% | 49.8% |
| Currently Married | 36.3% | 51.3% | 48.0% |
| Married but Separated | 2.2% | 0.9% | 1.8% |
| Single Population | 61.4% | 47.8% | 50.2% |
| Never Married | 48.8% | 27.5% | 33.8% |
| Divorced | 11.1% | 14.1% | 10.8% |
| Widowed | 1.5% | 6.2% | 5.6% |
| space5 | | | |
| Household Size | 2.89 | 2.46 | 2.60 |
| Households | 3,346 | 6,612 | 124,010,992 |
| Family Households | 2,051 | 4,283 | 80,755,759 |
| Married couple, w/children | 41.8% | 29.2% | 30.5% |
| Married couple, no children | 32.7% | 50.9% | 42.9% |
| Non Family Households | 1,295 | 2,329 | 43,255,233 |
| Single householder, w/children | 13.3% | 11.6% | 15.8% |
| Single householder, no children | 12.1% | 8.3% | 10.8% |