| | Darien, IL | Romeoville, IL | United States |
| Population | 22,087 | 40,099 | 329,725,481 |
| Female Population | 50.0% | 50.8% | 50.5% |
| Male Population | 50.0% | 49.2% | 49.5% |
| Median Age | 44.6 | 35.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 22,062 | 39,697 | 309,327,143 |
| Population - 2000 | 22,860 | 21,153 | 285,036,114 |
| Population - 1990 | 18,341 | 14,074 | 251,960,433 |
| Pop. 2000 to Now | -5.8% | 88.0% | 15.6% |
| Pop. 1990 to Now | 17.4% | 182.6% | 30.8% |
| space4 | | | |
| Population Density | 3,561.3 | 2,109.0 | 93.4 |
| Land Area | 6.2 | 19.0 | 3,531,905.4 |
| Water Area | 0.1 | 1.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Darien, IL | Romeoville, IL | United States |
| Age 0 to 4 | 3.2% | 5.8% | 5.9% |
| Age 5 to 9 | 5.5% | 5.7% | 6.1% |
| Age 10 to 14 | 6.1% | 6.4% | 6.6% |
| Age 15 to 17 | 3.9% | 5.6% | 3.9% |
| Age 18 to 20 | 2.6% | 6.3% | 4.0% |
| Age 21 to 24 | 4.8% | 6.7% | 5.2% |
| Age 25 to 34 | 11.8% | 12.8% | 13.8% |
| Age 35 to 44 | 12.7% | 13.6% | 12.9% |
| Age 45 to 54 | 12.2% | 14.9% | 12.6% |
| Age 55 to 59 | 8.0% | 6.7% | 6.7% |
| Age 60 to 64 | 7.7% | 4.6% | 6.3% |
| Age 65 to 74 | 14.1% | 6.4% | 9.6% |
| Age 75 to 84 | 5.4% | 3.2% | 4.5% |
| Age 85 and over | 1.9% | 1.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Darien, IL | Romeoville, IL | United States |
| White | 73.9% | 45.7% | 59.4% |
| Black | 3.3% | 11.1% | 12.2% |
| Asian | 12.2% | 5.8% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.2% | 0.4% |
| Two or More Races | 3.1% | 3.3% | 3.2% |
| Hispanic | 7.6% | 33.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Darien, IL | Romeoville, IL | United States |
| Married Population | 57.5% | 50.1% | 49.8% |
| Currently Married | 56.3% | 48.8% | 48.0% |
| Married but Separated | 1.2% | 1.3% | 1.8% |
| Single Population | 42.5% | 49.9% | 50.2% |
| Never Married | 26.7% | 36.7% | 33.8% |
| Divorced | 10.3% | 8.3% | 10.8% |
| Widowed | 5.4% | 4.8% | 5.6% |
| space5 | | | |
| Household Size | 2.52 | 3.24 | 2.60 |
| Households | 8,770 | 12,047 | 124,010,992 |
| Family Households | 6,340 | 9,079 | 80,755,759 |
| Married couple, w/children | 27.1% | 40.1% | 30.5% |
| Married couple, no children | 51.7% | 38.9% | 42.9% |
| Non Family Households | 2,430 | 2,968 | 43,255,233 |
| Single householder, w/children | 9.7% | 11.4% | 15.8% |
| Single householder, no children | 11.5% | 9.5% | 10.8% |