| | Sergeant Bluff, IA | Onawa, IA | United States |
| Population | 4,917 | 2,894 | 329,725,481 |
| Female Population | 51.2% | 54.2% | 50.5% |
| Male Population | 48.8% | 45.9% | 49.5% |
| Median Age | 35.3 | 38.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 4,322 | 3,001 | 309,327,143 |
| Population - 2000 | 3,321 | 3,091 | 285,036,114 |
| Population - 1990 | 2,772 | 2,936 | 251,960,433 |
| Pop. 2000 to Now | 54.1% | -10.5% | 15.6% |
| Pop. 1990 to Now | 84.7% | -5.8% | 30.8% |
| space4 | | | |
| Population Density | 1,672.5 | 557.8 | 93.4 |
| Land Area | 2.9 | 5.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Sergeant Bluff, IA | Onawa, IA | United States |
| Age 0 to 4 | 8.5% | 5.8% | 5.9% |
| Age 5 to 9 | 8.7% | 4.5% | 6.1% |
| Age 10 to 14 | 10.4% | 6.8% | 6.6% |
| Age 15 to 17 | 4.4% | 5.6% | 3.9% |
| Age 18 to 20 | 4.3% | 4.4% | 4.0% |
| Age 21 to 24 | 2.5% | 3.7% | 5.2% |
| Age 25 to 34 | 10.8% | 13.2% | 13.8% |
| Age 35 to 44 | 15.5% | 11.7% | 12.9% |
| Age 45 to 54 | 15.0% | 12.7% | 12.6% |
| Age 55 to 59 | 4.1% | 4.6% | 6.7% |
| Age 60 to 64 | 4.5% | 6.6% | 6.3% |
| Age 65 to 74 | 8.0% | 7.3% | 9.6% |
| Age 75 to 84 | 2.7% | 7.2% | 4.5% |
| Age 85 and over | 0.7% | 5.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Sergeant Bluff, IA | Onawa, IA | United States |
| White | 92.9% | 93.5% | 59.4% |
| Black | 0.0% | 0.1% | 12.2% |
| Asian | 0.9% | 0.0% | 5.6% |
| Native American | 0.0% | 1.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 1.1% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 2.2% | 1.5% | 3.2% |
| Hispanic | 3.9% | 2.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Sergeant Bluff, IA | Onawa, IA | United States |
| Married Population | 60.7% | 46.8% | 49.8% |
| Currently Married | 60.5% | 42.9% | 48.0% |
| Married but Separated | 0.2% | 3.9% | 1.8% |
| Single Population | 39.3% | 53.2% | 50.2% |
| Never Married | 26.4% | 27.5% | 33.8% |
| Divorced | 9.7% | 14.0% | 10.8% |
| Widowed | 3.2% | 11.7% | 5.6% |
| space5 | | | |
| Household Size | 2.86 | 2.32 | 2.60 |
| Households | 1,715 | 1,217 | 124,010,992 |
| Family Households | 1,407 | 693 | 80,755,759 |
| Married couple, w/children | 41.2% | 24.2% | 30.5% |
| Married couple, no children | 35.5% | 43.7% | 42.9% |
| Non Family Households | 308 | 524 | 43,255,233 |
| Single householder, w/children | 16.1% | 19.0% | 15.8% |
| Single householder, no children | 7.3% | 13.0% | 10.8% |