| | Flandreau, SD | Gallup, NM | United States |
| Population | 2,298 | 21,901 | 329,725,481 |
| Female Population | 51.4% | 50.2% | 50.5% |
| Male Population | 48.7% | 49.8% | 49.5% |
| Median Age | 36.8 | 34.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 2,339 | 21,795 | 309,327,143 |
| Population - 2000 | 2,376 | 20,209 | 285,036,114 |
| Population - 1990 | 2,311 | 19,154 | 251,960,433 |
| Pop. 2000 to Now | -3.5% | 5.2% | 15.6% |
| Pop. 1990 to Now | -0.8% | 11.0% | 30.8% |
| space4 | | | |
| Population Density | 1,236.2 | 1,095.6 | 93.4 |
| Land Area | 1.9 | 20.0 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Flandreau, SD | Gallup, NM | United States |
| Age 0 to 4 | 9.7% | 7.6% | 5.9% |
| Age 5 to 9 | 8.2% | 8.0% | 6.1% |
| Age 10 to 14 | 7.0% | 9.8% | 6.6% |
| Age 15 to 17 | 4.0% | 5.6% | 3.9% |
| Age 18 to 20 | 2.0% | 2.8% | 4.0% |
| Age 21 to 24 | 2.8% | 2.9% | 5.2% |
| Age 25 to 34 | 13.3% | 14.7% | 13.8% |
| Age 35 to 44 | 11.0% | 14.3% | 12.9% |
| Age 45 to 54 | 8.3% | 10.0% | 12.6% |
| Age 55 to 59 | 4.7% | 5.1% | 6.7% |
| Age 60 to 64 | 6.9% | 5.2% | 6.3% |
| Age 65 to 74 | 11.7% | 9.2% | 9.6% |
| Age 75 to 84 | 8.2% | 3.5% | 4.5% |
| Age 85 and over | 2.2% | 1.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Flandreau, SD | Gallup, NM | United States |
| White | 54.8% | 16.8% | 59.4% |
| Black | 1.9% | 1.4% | 12.2% |
| Asian | 5.4% | 3.4% | 5.6% |
| Native American | 20.9% | 44.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.2% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 11.5% | 2.0% | 3.2% |
| Hispanic | 5.5% | 31.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Flandreau, SD | Gallup, NM | United States |
| Married Population | 50.6% | 40.7% | 49.8% |
| Currently Married | 46.3% | 37.7% | 48.0% |
| Married but Separated | 4.2% | 3.1% | 1.8% |
| Single Population | 49.4% | 59.3% | 50.2% |
| Never Married | 27.2% | 42.5% | 33.8% |
| Divorced | 12.6% | 12.0% | 10.8% |
| Widowed | 9.7% | 4.7% | 5.6% |
| space5 | | | |
| Household Size | 2.48 | 2.92 | 2.60 |
| Households | 908 | 7,313 | 124,010,992 |
| Family Households | 524 | 4,896 | 80,755,759 |
| Married couple, w/children | 27.1% | 24.8% | 30.5% |
| Married couple, no children | 39.5% | 31.1% | 42.9% |
| Non Family Households | 384 | 2,417 | 43,255,233 |
| Single householder, w/children | 28.1% | 29.4% | 15.8% |
| Single householder, no children | 5.3% | 14.6% | 10.8% |