| | Darby, MT | Kansas City, MO | United States |
| Population | 609 | 502,597 | 329,725,481 |
| Female Population | 45.8% | 51.5% | 50.5% |
| Male Population | 54.2% | 48.5% | 49.5% |
| Median Age | 52.8 | 35.4 | 38.4 |
| space3 | | | |
| Population - 2010 | 721 | 460,690 | 309,327,143 |
| Population - 2000 | 710 | 441,545 | 285,036,114 |
| Population - 1990 | 625 | 435,146 | 251,960,433 |
| Pop. 2000 to Now | 16.2% | 12.6% | 15.6% |
| Pop. 1990 to Now | 32.0% | 14.3% | 30.8% |
| space4 | | | |
| Population Density | 998.4 | 1,596.1 | 93.4 |
| Land Area | 0.6 | 314.9 | 3,531,905.4 |
| Water Area | 0.0 | 4.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Darby, MT | Kansas City, MO | United States |
| Age 0 to 4 | 1.5% | 6.4% | 5.9% |
| Age 5 to 9 | 2.6% | 6.5% | 6.1% |
| Age 10 to 14 | 3.0% | 6.4% | 6.6% |
| Age 15 to 17 | 2.6% | 3.6% | 3.9% |
| Age 18 to 20 | 1.5% | 3.4% | 4.0% |
| Age 21 to 24 | 3.3% | 5.5% | 5.2% |
| Age 25 to 34 | 19.2% | 17.7% | 13.8% |
| Age 35 to 44 | 9.0% | 13.3% | 12.9% |
| Age 45 to 54 | 14.0% | 11.7% | 12.6% |
| Age 55 to 59 | 8.9% | 6.2% | 6.7% |
| Age 60 to 64 | 12.8% | 6.0% | 6.3% |
| Age 65 to 74 | 16.9% | 8.3% | 9.6% |
| Age 75 to 84 | 4.6% | 3.4% | 4.5% |
| Age 85 and over | 0.2% | 1.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Darby, MT | Kansas City, MO | United States |
| White | 86.4% | 55.5% | 59.4% |
| Black | 0.2% | 26.3% | 12.2% |
| Asian | 7.6% | 2.6% | 5.6% |
| Native American | 1.5% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.2% | 0.2% |
| Other | 0.0% | 0.4% | 0.4% |
| Two or More Races | 3.3% | 4.0% | 3.2% |
| Hispanic | 1.1% | 10.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Darby, MT | Kansas City, MO | United States |
| Married Population | 45.6% | 42.6% | 49.8% |
| Currently Married | 42.9% | 40.6% | 48.0% |
| Married but Separated | 2.7% | 2.0% | 1.8% |
| Single Population | 54.4% | 57.4% | 50.2% |
| Never Married | 26.7% | 39.3% | 33.8% |
| Divorced | 23.7% | 13.3% | 10.8% |
| Widowed | 4.1% | 4.8% | 5.6% |
| space5 | | | |
| Household Size | 1.88 | 2.31 | 2.60 |
| Households | 321 | 213,560 | 124,010,992 |
| Family Households | 164 | 114,540 | 80,755,759 |
| Married couple, w/children | 1.2% | 29.0% | 30.5% |
| Married couple, no children | 68.3% | 38.1% | 42.9% |
| Non Family Households | 157 | 99,020 | 43,255,233 |
| Single householder, w/children | 17.7% | 20.2% | 15.8% |
| Single householder, no children | 12.8% | 12.7% | 10.8% |