| | Gary, IN | Joliet, IL | United States |
| Population | 69,739 | 150,323 | 329,725,481 |
| Female Population | 54.2% | 50.2% | 50.5% |
| Male Population | 45.8% | 49.8% | 49.5% |
| Median Age | 37.1 | 33.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 80,159 | 147,521 | 309,327,143 |
| Population - 2000 | 102,746 | 106,221 | 285,036,114 |
| Population - 1990 | 116,646 | 76,836 | 251,960,433 |
| Pop. 2000 to Now | -27.3% | 38.1% | 15.6% |
| Pop. 1990 to Now | -36.0% | 90.9% | 30.8% |
| space4 | | | |
| Population Density | 1,402.7 | 2,344.3 | 93.4 |
| Land Area | 49.7 | 64.1 | 3,531,905.4 |
| Water Area | 7.5 | 0.7 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Gary, IN | Joliet, IL | United States |
| Age 0 to 4 | 7.1% | 6.4% | 5.9% |
| Age 5 to 9 | 7.8% | 7.3% | 6.1% |
| Age 10 to 14 | 7.8% | 8.8% | 6.6% |
| Age 15 to 17 | 4.5% | 4.8% | 3.9% |
| Age 18 to 20 | 3.9% | 5.1% | 4.0% |
| Age 21 to 24 | 4.4% | 5.7% | 5.2% |
| Age 25 to 34 | 11.6% | 13.5% | 13.8% |
| Age 35 to 44 | 11.7% | 13.9% | 12.9% |
| Age 45 to 54 | 10.2% | 14.6% | 12.6% |
| Age 55 to 59 | 6.1% | 5.7% | 6.7% |
| Age 60 to 64 | 6.3% | 4.2% | 6.3% |
| Age 65 to 74 | 11.5% | 6.3% | 9.6% |
| Age 75 to 84 | 4.9% | 2.6% | 4.5% |
| Age 85 and over | 2.2% | 1.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Gary, IN | Joliet, IL | United States |
| White | 9.9% | 44.9% | 59.4% |
| Black | 77.9% | 16.8% | 12.2% |
| Asian | 0.3% | 1.7% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.3% | 0.4% |
| Two or More Races | 2.8% | 2.5% | 3.2% |
| Hispanic | 8.6% | 33.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Gary, IN | Joliet, IL | United States |
| Married Population | 29.6% | 47.3% | 49.8% |
| Currently Married | 26.0% | 45.8% | 48.0% |
| Married but Separated | 3.5% | 1.5% | 1.8% |
| Single Population | 70.4% | 52.7% | 50.2% |
| Never Married | 46.7% | 38.7% | 33.8% |
| Divorced | 15.0% | 10.0% | 10.8% |
| Widowed | 8.7% | 4.0% | 5.6% |
| space5 | | | |
| Household Size | 2.49 | 2.98 | 2.60 |
| Households | 27,773 | 49,563 | 124,010,992 |
| Family Households | 16,519 | 34,947 | 80,755,759 |
| Married couple, w/children | 10.4% | 39.6% | 30.5% |
| Married couple, no children | 26.8% | 30.8% | 42.9% |
| Non Family Households | 11,254 | 14,616 | 43,255,233 |
| Single householder, w/children | 41.2% | 19.4% | 15.8% |
| Single householder, no children | 21.6% | 10.2% | 10.8% |