| | Markham, IL | Rockford, IL | United States |
| Population | 11,733 | 148,942 | 329,725,481 |
| Female Population | 52.9% | 51.1% | 50.5% |
| Male Population | 47.1% | 48.9% | 49.5% |
| Median Age | 32.2 | 37.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 12,546 | 153,173 | 309,327,143 |
| Population - 2000 | 12,620 | 150,115 | 285,036,114 |
| Population - 1990 | 13,136 | 139,426 | 251,960,433 |
| Pop. 2000 to Now | -3.6% | -3.5% | 15.6% |
| Pop. 1990 to Now | -7.4% | 3.9% | 30.8% |
| space4 | | | |
| Population Density | 2,170.8 | 2,313.9 | 93.4 |
| Land Area | 5.4 | 64.4 | 3,531,905.4 |
| Water Area | 0.0 | 1.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Markham, IL | Rockford, IL | United States |
| Age 0 to 4 | 9.1% | 6.8% | 5.9% |
| Age 5 to 9 | 8.5% | 6.8% | 6.1% |
| Age 10 to 14 | 8.9% | 7.3% | 6.6% |
| Age 15 to 17 | 3.6% | 4.1% | 3.9% |
| Age 18 to 20 | 4.6% | 3.2% | 4.0% |
| Age 21 to 24 | 4.9% | 5.3% | 5.2% |
| Age 25 to 34 | 13.8% | 13.3% | 13.8% |
| Age 35 to 44 | 12.3% | 11.9% | 12.9% |
| Age 45 to 54 | 9.6% | 11.7% | 12.6% |
| Age 55 to 59 | 7.1% | 6.6% | 6.7% |
| Age 60 to 64 | 4.1% | 6.2% | 6.3% |
| Age 65 to 74 | 8.6% | 9.5% | 9.6% |
| Age 75 to 84 | 3.2% | 4.1% | 4.5% |
| Age 85 and over | 1.7% | 3.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Markham, IL | Rockford, IL | United States |
| White | 12.2% | 52.5% | 59.4% |
| Black | 75.1% | 21.0% | 12.2% |
| Asian | 0.3% | 3.5% | 5.6% |
| Native American | 0.2% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.2% | 0.4% |
| Two or More Races | 0.9% | 3.7% | 3.2% |
| Hispanic | 11.2% | 18.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Markham, IL | Rockford, IL | United States |
| Married Population | 29.8% | 41.9% | 49.8% |
| Currently Married | 27.1% | 39.8% | 48.0% |
| Married but Separated | 2.7% | 2.1% | 1.8% |
| Single Population | 70.2% | 58.1% | 50.2% |
| Never Married | 52.1% | 37.7% | 33.8% |
| Divorced | 12.4% | 13.8% | 10.8% |
| Widowed | 5.7% | 6.5% | 5.6% |
| space5 | | | |
| Household Size | 3.25 | 2.37 | 2.60 |
| Households | 3,607 | 61,304 | 124,010,992 |
| Family Households | 2,574 | 36,078 | 80,755,759 |
| Married couple, w/children | 11.0% | 22.5% | 30.5% |
| Married couple, no children | 29.3% | 38.4% | 42.9% |
| Non Family Households | 1,033 | 25,226 | 43,255,233 |
| Single householder, w/children | 37.4% | 26.5% | 15.8% |
| Single householder, no children | 22.3% | 12.7% | 10.8% |