| | Garretson, SD | Flandreau, SD | United States |
| Population | 1,367 | 2,298 | 329,725,481 |
| Female Population | 55.0% | 51.4% | 50.5% |
| Male Population | 45.0% | 48.7% | 49.5% |
| Median Age | 41.6 | 36.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 1,170 | 2,339 | 309,327,143 |
| Population - 2000 | 1,165 | 2,376 | 285,036,114 |
| Population - 1990 | 924 | 2,311 | 251,960,433 |
| Pop. 2000 to Now | -1.6% | -3.5% | 15.6% |
| Pop. 1990 to Now | 24.1% | -0.8% | 30.8% |
| space4 | | | |
| Population Density | 938.9 | 1,236.2 | 93.4 |
| Land Area | 1.5 | 1.9 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Garretson, SD | Flandreau, SD | United States |
| Age 0 to 4 | 9.3% | 9.7% | 5.9% |
| Age 5 to 9 | 8.1% | 8.2% | 6.1% |
| Age 10 to 14 | 4.5% | 7.0% | 6.6% |
| Age 15 to 17 | 4.0% | 4.0% | 3.9% |
| Age 18 to 20 | 2.3% | 2.0% | 4.0% |
| Age 21 to 24 | 1.7% | 2.8% | 5.2% |
| Age 25 to 34 | 15.1% | 13.3% | 13.8% |
| Age 35 to 44 | 8.3% | 11.0% | 12.9% |
| Age 45 to 54 | 11.7% | 8.3% | 12.6% |
| Age 55 to 59 | 8.2% | 4.7% | 6.7% |
| Age 60 to 64 | 9.3% | 6.9% | 6.3% |
| Age 65 to 74 | 7.9% | 11.7% | 9.6% |
| Age 75 to 84 | 3.0% | 8.2% | 4.5% |
| Age 85 and over | 6.7% | 2.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Garretson, SD | Flandreau, SD | United States |
| White | 83.1% | 54.8% | 59.4% |
| Black | 0.7% | 1.9% | 12.2% |
| Asian | 0.0% | 5.4% | 5.6% |
| Native American | 13.0% | 20.9% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 2.2% | 11.5% | 3.2% |
| Hispanic | 1.0% | 5.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Garretson, SD | Flandreau, SD | United States |
| Married Population | 51.7% | 50.6% | 49.8% |
| Currently Married | 51.2% | 46.3% | 48.0% |
| Married but Separated | 0.5% | 4.2% | 1.8% |
| Single Population | 48.3% | 49.4% | 50.2% |
| Never Married | 22.0% | 27.2% | 33.8% |
| Divorced | 18.2% | 12.6% | 10.8% |
| Widowed | 8.1% | 9.7% | 5.6% |
| space5 | | | |
| Household Size | 2.35 | 2.48 | 2.60 |
| Households | 565 | 908 | 124,010,992 |
| Family Households | 331 | 524 | 80,755,759 |
| Married couple, w/children | 36.6% | 27.1% | 30.5% |
| Married couple, no children | 43.5% | 39.5% | 42.9% |
| Non Family Households | 234 | 384 | 43,255,233 |
| Single householder, w/children | 9.1% | 28.1% | 15.8% |
| Single householder, no children | 10.9% | 5.3% | 10.8% |