| | Marion, KS | Olathe, KS | United States |
| Population | 1,852 | 140,339 | 329,725,481 |
| Female Population | 52.4% | 50.2% | 50.5% |
| Male Population | 47.6% | 49.8% | 49.5% |
| Median Age | 44.2 | 35.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 1,928 | 126,253 | 309,327,143 |
| Population - 2000 | 2,110 | 92,962 | 285,036,114 |
| Population - 1990 | 1,906 | 63,352 | 251,960,433 |
| Pop. 2000 to Now | -17.6% | 52.4% | 15.6% |
| Pop. 1990 to Now | -8.8% | 123.6% | 30.8% |
| space4 | | | |
| Population Density | 690.8 | 2,277.3 | 93.4 |
| Land Area | 2.7 | 61.6 | 3,531,905.4 |
| Water Area | 0.0 | 0.8 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Marion, KS | Olathe, KS | United States |
| Age 0 to 4 | 7.7% | 6.5% | 5.9% |
| Age 5 to 9 | 7.5% | 8.3% | 6.1% |
| Age 10 to 14 | 4.3% | 8.0% | 6.6% |
| Age 15 to 17 | 3.9% | 4.8% | 3.9% |
| Age 18 to 20 | 0.9% | 3.5% | 4.0% |
| Age 21 to 24 | 2.6% | 4.2% | 5.2% |
| Age 25 to 34 | 15.0% | 12.9% | 13.8% |
| Age 35 to 44 | 9.7% | 15.9% | 12.9% |
| Age 45 to 54 | 11.6% | 13.5% | 12.6% |
| Age 55 to 59 | 6.4% | 5.8% | 6.7% |
| Age 60 to 64 | 3.3% | 4.7% | 6.3% |
| Age 65 to 74 | 13.5% | 7.5% | 9.6% |
| Age 75 to 84 | 8.9% | 3.2% | 4.5% |
| Age 85 and over | 4.9% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Marion, KS | Olathe, KS | United States |
| White | 92.1% | 74.9% | 59.4% |
| Black | 1.1% | 5.8% | 12.2% |
| Asian | 0.4% | 4.2% | 5.6% |
| Native American | 0.4% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.4% | 0.4% |
| Two or More Races | 0.6% | 3.2% | 3.2% |
| Hispanic | 5.3% | 11.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Marion, KS | Olathe, KS | United States |
| Married Population | 50.7% | 59.4% | 49.8% |
| Currently Married | 50.1% | 58.4% | 48.0% |
| Married but Separated | 0.5% | 1.0% | 1.8% |
| Single Population | 49.3% | 40.6% | 50.2% |
| Never Married | 19.6% | 27.3% | 33.8% |
| Divorced | 15.1% | 9.7% | 10.8% |
| Widowed | 14.5% | 3.6% | 5.6% |
| space5 | | | |
| Household Size | 2.10 | 2.77 | 2.60 |
| Households | 861 | 50,141 | 124,010,992 |
| Family Households | 498 | 37,203 | 80,755,759 |
| Married couple, w/children | 28.9% | 40.9% | 30.5% |
| Married couple, no children | 51.8% | 40.3% | 42.9% |
| Non Family Households | 363 | 12,938 | 43,255,233 |
| Single householder, w/children | 19.3% | 12.3% | 15.8% |
| Single householder, no children | 0.0% | 6.4% | 10.8% |