| | Eureka, SD | Phoenix, AZ | United States |
| Population | 895 | 1,591,119 | 329,725,481 |
| Female Population | 55.9% | 49.7% | 50.5% |
| Male Population | 44.1% | 50.3% | 49.5% |
| Median Age | 58.3 | 34.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 864 | 1,448,998 | 309,327,143 |
| Population - 2000 | 1,101 | 1,321,045 | 285,036,114 |
| Population - 1990 | 1,197 | 983,403 | 251,960,433 |
| Pop. 2000 to Now | -25.8% | 29.3% | 15.6% |
| Pop. 1990 to Now | -31.8% | 73.7% | 30.8% |
| space4 | | | |
| Population Density | 959.3 | 3,073.6 | 93.4 |
| Land Area | 0.9 | 517.7 | 3,531,905.4 |
| Water Area | 0.1 | 1.3 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Eureka, SD | Phoenix, AZ | United States |
| Age 0 to 4 | 2.6% | 6.8% | 5.9% |
| Age 5 to 9 | 8.6% | 6.8% | 6.1% |
| Age 10 to 14 | 2.8% | 7.4% | 6.6% |
| Age 15 to 17 | 2.3% | 4.3% | 3.9% |
| Age 18 to 20 | 4.5% | 4.1% | 4.0% |
| Age 21 to 24 | 5.6% | 5.7% | 5.2% |
| Age 25 to 34 | 10.8% | 16.2% | 13.8% |
| Age 35 to 44 | 5.0% | 13.9% | 12.9% |
| Age 45 to 54 | 6.4% | 12.6% | 12.6% |
| Age 55 to 59 | 8.5% | 6.0% | 6.7% |
| Age 60 to 64 | 4.0% | 5.1% | 6.3% |
| Age 65 to 74 | 12.7% | 7.0% | 9.6% |
| Age 75 to 84 | 14.4% | 2.9% | 4.5% |
| Age 85 and over | 11.7% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Eureka, SD | Phoenix, AZ | United States |
| White | 92.6% | 41.4% | 59.4% |
| Black | 3.4% | 6.9% | 12.2% |
| Asian | 0.7% | 3.8% | 5.6% |
| Native American | 0.2% | 1.6% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.2% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 2.8% | 3.2% | 3.2% |
| Hispanic | 0.2% | 42.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Eureka, SD | Phoenix, AZ | United States |
| Married Population | 47.5% | 44.7% | 49.8% |
| Currently Married | 46.6% | 42.5% | 48.0% |
| Married but Separated | 0.9% | 2.1% | 1.8% |
| Single Population | 52.5% | 55.3% | 50.2% |
| Never Married | 29.9% | 39.1% | 33.8% |
| Divorced | 10.4% | 12.2% | 10.8% |
| Widowed | 12.2% | 4.0% | 5.6% |
| space5 | | | |
| Household Size | 2.09 | 2.71 | 2.60 |
| Households | 387 | 579,876 | 124,010,992 |
| Family Households | 176 | 368,588 | 80,755,759 |
| Married couple, w/children | 18.2% | 31.6% | 30.5% |
| Married couple, no children | 63.1% | 33.6% | 42.9% |
| Non Family Households | 211 | 211,288 | 43,255,233 |
| Single householder, w/children | 14.8% | 22.5% | 15.8% |
| Single householder, no children | 4.0% | 12.3% | 10.8% |