| Statistic | Keystone | South Dakota | National |
| Population | 542 | 884,659 | 328,239,523 |
| Population density (sq mi) | 181 | 12 | 91 |
| Median age | 30.0 | 36.8 | 37.7 |
| Male/Female ratio | 1.2:1 | 1.0:1 | 1.0:1 |
| Married (15yrs & older) | 45% | 59% | 55% |
| Families w/ Kids under 18 | 49% | 44% | 43% |
| Speak English | 78% | 94% | 79% |
| Speak Spanish | 19% | 2% | 13% |
| Race | Keystone | South Dakota | National |
| White | 87.64% | 84.77% | 73.35% |
| Black | 0.00% | 1.65% | 12.63% |
| Asian | 0.92% | 1.33% | 5.22% |
| American Indian | 2.03% | 8.72% | 0.82% |
| Native Hawaiian | 0.37% | 0.04% | 0.18% |
| Mixed race | 8.67% | 2.61% | 3.06% |
| Other race | 0.37% | 0.88% | 4.75% |
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