| | Selby, SD | Eugene, OR | United States |
| Population | 612 | 173,278 | 329,725,481 |
| Female Population | 53.4% | 51.0% | 50.5% |
| Male Population | 46.6% | 49.0% | 49.5% |
| Median Age | 47.5 | 35.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 636 | 156,516 | 309,327,143 |
| Population - 2000 | 736 | 137,893 | 285,036,114 |
| Population - 1990 | 707 | 112,669 | 251,960,433 |
| Pop. 2000 to Now | -16.9% | 25.6% | 15.6% |
| Pop. 1990 to Now | -13.4% | 53.8% | 30.8% |
| space4 | | | |
| Population Density | 859.6 | 3,923.9 | 93.4 |
| Land Area | 0.7 | 44.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Selby, SD | Eugene, OR | United States |
| Age 0 to 4 | 6.5% | 4.1% | 5.9% |
| Age 5 to 9 | 5.9% | 4.6% | 6.1% |
| Age 10 to 14 | 7.2% | 5.1% | 6.6% |
| Age 15 to 17 | 2.9% | 3.1% | 3.9% |
| Age 18 to 20 | 1.3% | 8.3% | 4.0% |
| Age 21 to 24 | 2.9% | 9.8% | 5.2% |
| Age 25 to 34 | 9.8% | 14.9% | 13.8% |
| Age 35 to 44 | 12.9% | 12.7% | 12.9% |
| Age 45 to 54 | 6.4% | 10.3% | 12.6% |
| Age 55 to 59 | 7.2% | 5.5% | 6.7% |
| Age 60 to 64 | 8.8% | 5.2% | 6.3% |
| Age 65 to 74 | 6.5% | 10.3% | 9.6% |
| Age 75 to 84 | 12.6% | 4.2% | 4.5% |
| Age 85 and over | 9.0% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Selby, SD | Eugene, OR | United States |
| White | 81.9% | 77.3% | 59.4% |
| Black | 0.0% | 1.3% | 12.2% |
| Asian | 0.0% | 4.0% | 5.6% |
| Native American | 3.3% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.3% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 6.7% | 5.8% | 3.2% |
| Hispanic | 8.2% | 10.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Selby, SD | Eugene, OR | United States |
| Married Population | 61.4% | 39.5% | 49.8% |
| Currently Married | 60.2% | 38.3% | 48.0% |
| Married but Separated | 1.2% | 1.2% | 1.8% |
| Single Population | 38.6% | 60.5% | 50.2% |
| Never Married | 16.1% | 44.1% | 33.8% |
| Divorced | 8.7% | 12.5% | 10.8% |
| Widowed | 13.8% | 3.9% | 5.6% |
| space5 | | | |
| Household Size | 2.37 | 2.27 | 2.60 |
| Households | 231 | 73,466 | 124,010,992 |
| Family Households | 152 | 36,743 | 80,755,759 |
| Married couple, w/children | 37.5% | 27.3% | 30.5% |
| Married couple, no children | 52.0% | 45.5% | 42.9% |
| Non Family Households | 79 | 36,723 | 43,255,233 |
| Single householder, w/children | 0.0% | 18.2% | 15.8% |
| Single householder, no children | 10.5% | 8.9% | 10.8% |