| | Greenfield, IA | Oskaloosa, IA | United States |
| Population | 1,671 | 11,552 | 329,725,481 |
| Female Population | 46.6% | 50.4% | 50.5% |
| Male Population | 53.4% | 49.6% | 49.5% |
| Median Age | 53.5 | 35.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 1,986 | 11,518 | 309,327,143 |
| Population - 2000 | 2,129 | 10,938 | 285,036,114 |
| Population - 1990 | 2,074 | 10,632 | 251,960,433 |
| Pop. 2000 to Now | -14.9% | 7.9% | 15.6% |
| Pop. 1990 to Now | -12.6% | 11.0% | 30.8% |
| space4 | | | |
| Population Density | 921.2 | 1,440.0 | 93.4 |
| Land Area | 1.8 | 8.0 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Greenfield, IA | Oskaloosa, IA | United States |
| Age 0 to 4 | 3.8% | 6.8% | 5.9% |
| Age 5 to 9 | 5.4% | 6.6% | 6.1% |
| Age 10 to 14 | 4.0% | 6.9% | 6.6% |
| Age 15 to 17 | 2.9% | 3.6% | 3.9% |
| Age 18 to 20 | 1.7% | 5.2% | 4.0% |
| Age 21 to 24 | 5.6% | 5.8% | 5.2% |
| Age 25 to 34 | 11.6% | 14.8% | 13.8% |
| Age 35 to 44 | 6.7% | 10.6% | 12.9% |
| Age 45 to 54 | 9.9% | 10.5% | 12.6% |
| Age 55 to 59 | 6.8% | 4.6% | 6.7% |
| Age 60 to 64 | 10.4% | 5.5% | 6.3% |
| Age 65 to 74 | 13.2% | 10.6% | 9.6% |
| Age 75 to 84 | 10.8% | 5.2% | 4.5% |
| Age 85 and over | 7.2% | 3.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Greenfield, IA | Oskaloosa, IA | United States |
| White | 97.4% | 89.4% | 59.4% |
| Black | 1.5% | 2.7% | 12.2% |
| Asian | 0.0% | 2.2% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.3% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 1.1% | 1.7% | 3.2% |
| Hispanic | 0.0% | 3.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Greenfield, IA | Oskaloosa, IA | United States |
| Married Population | 43.9% | 49.5% | 49.8% |
| Currently Married | 43.4% | 48.2% | 48.0% |
| Married but Separated | 0.5% | 1.4% | 1.8% |
| Single Population | 56.1% | 50.5% | 50.2% |
| Never Married | 26.5% | 31.0% | 33.8% |
| Divorced | 15.2% | 12.3% | 10.8% |
| Widowed | 14.4% | 7.1% | 5.6% |
| space5 | | | |
| Household Size | 1.81 | 2.36 | 2.60 |
| Households | 901 | 4,648 | 124,010,992 |
| Family Households | 356 | 2,887 | 80,755,759 |
| Married couple, w/children | 24.4% | 29.8% | 30.5% |
| Married couple, no children | 53.7% | 44.8% | 42.9% |
| Non Family Households | 545 | 1,761 | 43,255,233 |
| Single householder, w/children | 15.7% | 20.1% | 15.8% |
| Single householder, no children | 6.2% | 5.3% | 10.8% |