| | Fairfield, CA | Eugene, OR | United States |
| Population | 118,932 | 173,278 | 329,725,481 |
| Female Population | 50.1% | 51.0% | 50.5% |
| Male Population | 49.9% | 49.0% | 49.5% |
| Median Age | 35.2 | 35.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 105,652 | 156,516 | 309,327,143 |
| Population - 2000 | 96,178 | 137,893 | 285,036,114 |
| Population - 1990 | 77,211 | 112,669 | 251,960,433 |
| Pop. 2000 to Now | 22.3% | 25.6% | 15.6% |
| Pop. 1990 to Now | 52.3% | 53.8% | 30.8% |
| space4 | | | |
| Population Density | 2,899.5 | 3,923.9 | 93.4 |
| Land Area | 41.0 | 44.2 | 3,531,905.4 |
| Water Area | 0.3 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Fairfield, CA | Eugene, OR | United States |
| Age 0 to 4 | 7.4% | 4.1% | 5.9% |
| Age 5 to 9 | 6.2% | 4.6% | 6.1% |
| Age 10 to 14 | 7.6% | 5.1% | 6.6% |
| Age 15 to 17 | 4.1% | 3.1% | 3.9% |
| Age 18 to 20 | 3.6% | 8.3% | 4.0% |
| Age 21 to 24 | 5.4% | 9.8% | 5.2% |
| Age 25 to 34 | 15.5% | 14.9% | 13.8% |
| Age 35 to 44 | 13.7% | 12.7% | 12.9% |
| Age 45 to 54 | 12.3% | 10.3% | 12.6% |
| Age 55 to 59 | 5.7% | 5.5% | 6.7% |
| Age 60 to 64 | 5.5% | 5.2% | 6.3% |
| Age 65 to 74 | 7.8% | 10.3% | 9.6% |
| Age 75 to 84 | 3.7% | 4.2% | 4.5% |
| Age 85 and over | 1.5% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Fairfield, CA | Eugene, OR | United States |
| White | 29.0% | 77.3% | 59.4% |
| Black | 15.6% | 1.3% | 12.2% |
| Asian | 17.4% | 4.0% | 5.6% |
| Native American | 0.5% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 1.2% | 0.3% | 0.2% |
| Other | 0.4% | 0.3% | 0.4% |
| Two or More Races | 6.7% | 5.8% | 3.2% |
| Hispanic | 29.3% | 10.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Fairfield, CA | Eugene, OR | United States |
| Married Population | 51.5% | 39.5% | 49.8% |
| Currently Married | 49.2% | 38.3% | 48.0% |
| Married but Separated | 2.3% | 1.2% | 1.8% |
| Single Population | 48.5% | 60.5% | 50.2% |
| Never Married | 35.1% | 44.1% | 33.8% |
| Divorced | 8.6% | 12.5% | 10.8% |
| Widowed | 4.9% | 3.9% | 5.6% |
| space5 | | | |
| Household Size | 3.16 | 2.27 | 2.60 |
| Households | 37,176 | 73,466 | 124,010,992 |
| Family Households | 28,037 | 36,743 | 80,755,759 |
| Married couple, w/children | 34.1% | 27.3% | 30.5% |
| Married couple, no children | 37.1% | 45.5% | 42.9% |
| Non Family Households | 9,139 | 36,723 | 43,255,233 |
| Single householder, w/children | 17.8% | 18.2% | 15.8% |
| Single householder, no children | 11.0% | 8.9% | 10.8% |