| | Leavenworth, KS | Oswego, IL | United States |
| Population | 37,216 | 34,324 | 329,725,481 |
| Female Population | 45.5% | 51.7% | 50.5% |
| Male Population | 54.5% | 48.3% | 49.5% |
| Median Age | 36.9 | 39.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 35,380 | 30,659 | 309,327,143 |
| Population - 2000 | 35,420 | 13,326 | 285,036,114 |
| Population - 1990 | 38,495 | 3,876 | 251,960,433 |
| Pop. 2000 to Now | 1.5% | 175.4% | 15.6% |
| Pop. 1990 to Now | -6.7% | 846.8% | 30.8% |
| space4 | | | |
| Population Density | 1,518.9 | 2,305.5 | 93.4 |
| Land Area | 24.5 | 14.9 | 3,531,905.4 |
| Water Area | 0.1 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Leavenworth, KS | Oswego, IL | United States |
| Age 0 to 4 | 7.5% | 6.8% | 5.9% |
| Age 5 to 9 | 7.3% | 7.8% | 6.1% |
| Age 10 to 14 | 5.8% | 8.5% | 6.6% |
| Age 15 to 17 | 2.7% | 5.7% | 3.9% |
| Age 18 to 20 | 3.3% | 3.2% | 4.0% |
| Age 21 to 24 | 6.3% | 4.9% | 5.2% |
| Age 25 to 34 | 13.5% | 8.9% | 13.8% |
| Age 35 to 44 | 15.9% | 15.5% | 12.9% |
| Age 45 to 54 | 11.3% | 15.0% | 12.6% |
| Age 55 to 59 | 7.0% | 8.4% | 6.7% |
| Age 60 to 64 | 5.9% | 4.6% | 6.3% |
| Age 65 to 74 | 8.3% | 6.5% | 9.6% |
| Age 75 to 84 | 4.2% | 2.9% | 4.5% |
| Age 85 and over | 1.0% | 1.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Leavenworth, KS | Oswego, IL | United States |
| White | 70.6% | 66.7% | 59.4% |
| Black | 11.1% | 8.0% | 12.2% |
| Asian | 1.7% | 3.1% | 5.6% |
| Native American | 0.6% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.0% | 0.2% |
| Other | 0.5% | 0.0% | 0.4% |
| Two or More Races | 7.0% | 4.3% | 3.2% |
| Hispanic | 8.5% | 17.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Leavenworth, KS | Oswego, IL | United States |
| Married Population | 52.2% | 61.7% | 49.8% |
| Currently Married | 49.4% | 60.1% | 48.0% |
| Married but Separated | 2.7% | 1.5% | 1.8% |
| Single Population | 47.8% | 38.3% | 50.2% |
| Never Married | 28.5% | 26.8% | 33.8% |
| Divorced | 13.9% | 8.5% | 10.8% |
| Widowed | 5.3% | 3.1% | 5.6% |
| space5 | | | |
| Household Size | 2.49 | 2.92 | 2.60 |
| Households | 13,554 | 11,738 | 124,010,992 |
| Family Households | 8,504 | 9,610 | 80,755,759 |
| Married couple, w/children | 34.2% | 42.9% | 30.5% |
| Married couple, no children | 44.1% | 39.8% | 42.9% |
| Non Family Households | 5,050 | 2,128 | 43,255,233 |
| Single householder, w/children | 16.0% | 10.8% | 15.8% |
| Single householder, no children | 5.8% | 6.6% | 10.8% |