| | Decatur, NE | Onawa, IA | United States |
| Population | 507 | 2,894 | 329,725,481 |
| Female Population | 51.3% | 54.2% | 50.5% |
| Male Population | 48.7% | 45.9% | 49.5% |
| Median Age | 60.7 | 38.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 480 | 3,001 | 309,327,143 |
| Population - 2000 | 618 | 3,091 | 285,036,114 |
| Population - 1990 | 641 | 2,936 | 251,960,433 |
| Pop. 2000 to Now | -25.2% | -10.5% | 15.6% |
| Pop. 1990 to Now | -27.9% | -5.8% | 30.8% |
| space4 | | | |
| Population Density | 494.6 | 557.8 | 93.4 |
| Land Area | 1.0 | 5.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Decatur, NE | Onawa, IA | United States |
| Age 0 to 4 | 1.0% | 5.8% | 5.9% |
| Age 5 to 9 | 1.2% | 4.5% | 6.1% |
| Age 10 to 14 | 1.0% | 6.8% | 6.6% |
| Age 15 to 17 | 1.4% | 5.6% | 3.9% |
| Age 18 to 20 | 1.8% | 4.4% | 4.0% |
| Age 21 to 24 | 9.1% | 3.7% | 5.2% |
| Age 25 to 34 | 10.5% | 13.2% | 13.8% |
| Age 35 to 44 | 4.9% | 11.7% | 12.9% |
| Age 45 to 54 | 10.1% | 12.7% | 12.6% |
| Age 55 to 59 | 6.3% | 4.6% | 6.7% |
| Age 60 to 64 | 16.0% | 6.6% | 6.3% |
| Age 65 to 74 | 21.5% | 7.3% | 9.6% |
| Age 75 to 84 | 9.5% | 7.2% | 4.5% |
| Age 85 and over | 5.9% | 5.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Decatur, NE | Onawa, IA | United States |
| White | 89.3% | 93.5% | 59.4% |
| Black | 0.0% | 0.1% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 4.7% | 1.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 1.1% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 0.0% | 1.5% | 3.2% |
| Hispanic | 5.9% | 2.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Decatur, NE | Onawa, IA | United States |
| Married Population | 36.7% | 46.8% | 49.8% |
| Currently Married | 34.8% | 42.9% | 48.0% |
| Married but Separated | 1.8% | 3.9% | 1.8% |
| Single Population | 63.3% | 53.2% | 50.2% |
| Never Married | 30.3% | 27.5% | 33.8% |
| Divorced | 21.6% | 14.0% | 10.8% |
| Widowed | 11.4% | 11.7% | 5.6% |
| space5 | | | |
| Household Size | 2.00 | 2.32 | 2.60 |
| Households | 253 | 1,217 | 124,010,992 |
| Family Households | 120 | 693 | 80,755,759 |
| Married couple, w/children | 4.2% | 24.2% | 30.5% |
| Married couple, no children | 63.3% | 43.7% | 42.9% |
| Non Family Households | 133 | 524 | 43,255,233 |
| Single householder, w/children | 9.2% | 19.0% | 15.8% |
| Single householder, no children | 23.3% | 13.0% | 10.8% |