| | Joliet, IL | Mount Prospect, IL | United States |
| Population | 150,323 | 56,510 | 329,725,481 |
| Female Population | 50.2% | 50.2% | 50.5% |
| Male Population | 49.8% | 49.9% | 49.5% |
| Median Age | 33.6 | 40.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 147,521 | 55,082 | 309,327,143 |
| Population - 2000 | 106,221 | 56,265 | 285,036,114 |
| Population - 1990 | 76,836 | 53,170 | 251,960,433 |
| Pop. 2000 to Now | 38.1% | -5.3% | 15.6% |
| Pop. 1990 to Now | 90.9% | 0.2% | 30.8% |
| space4 | | | |
| Population Density | 2,344.3 | 5,272.0 | 93.4 |
| Land Area | 64.1 | 10.7 | 3,531,905.4 |
| Water Area | 0.7 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Joliet, IL | Mount Prospect, IL | United States |
| Age 0 to 4 | 6.4% | 6.9% | 5.9% |
| Age 5 to 9 | 7.3% | 5.5% | 6.1% |
| Age 10 to 14 | 8.8% | 6.6% | 6.6% |
| Age 15 to 17 | 4.8% | 3.9% | 3.9% |
| Age 18 to 20 | 5.1% | 2.5% | 4.0% |
| Age 21 to 24 | 5.7% | 2.9% | 5.2% |
| Age 25 to 34 | 13.5% | 13.4% | 13.8% |
| Age 35 to 44 | 13.9% | 14.0% | 12.9% |
| Age 45 to 54 | 14.6% | 14.6% | 12.6% |
| Age 55 to 59 | 5.7% | 5.9% | 6.7% |
| Age 60 to 64 | 4.2% | 6.1% | 6.3% |
| Age 65 to 74 | 6.3% | 9.3% | 9.6% |
| Age 75 to 84 | 2.6% | 5.9% | 4.5% |
| Age 85 and over | 1.0% | 2.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Joliet, IL | Mount Prospect, IL | United States |
| White | 44.9% | 64.5% | 59.4% |
| Black | 16.8% | 3.1% | 12.2% |
| Asian | 1.7% | 13.7% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.2% | 0.4% |
| Two or More Races | 2.5% | 2.2% | 3.2% |
| Hispanic | 33.8% | 16.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Joliet, IL | Mount Prospect, IL | United States |
| Married Population | 47.3% | 60.6% | 49.8% |
| Currently Married | 45.8% | 59.4% | 48.0% |
| Married but Separated | 1.5% | 1.1% | 1.8% |
| Single Population | 52.7% | 39.4% | 50.2% |
| Never Married | 38.7% | 26.2% | 33.8% |
| Divorced | 10.0% | 7.0% | 10.8% |
| Widowed | 4.0% | 6.2% | 5.6% |
| space5 | | | |
| Household Size | 2.98 | 2.60 | 2.60 |
| Households | 49,563 | 21,666 | 124,010,992 |
| Family Households | 34,947 | 15,235 | 80,755,759 |
| Married couple, w/children | 39.6% | 38.6% | 30.5% |
| Married couple, no children | 30.8% | 44.8% | 42.9% |
| Non Family Households | 14,616 | 6,431 | 43,255,233 |
| Single householder, w/children | 19.4% | 8.3% | 15.8% |
| Single householder, no children | 10.2% | 8.3% | 10.8% |