| | Johnston City, IL | Centralia, IL | United States |
| Population | 3,403 | 12,061 | 329,725,481 |
| Female Population | 44.0% | 51.9% | 50.5% |
| Male Population | 56.0% | 48.1% | 49.5% |
| Median Age | 41.3 | 40.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,563 | 13,028 | 309,327,143 |
| Population - 2000 | 3,557 | 14,136 | 285,036,114 |
| Population - 1990 | 3,706 | 14,274 | 251,960,433 |
| Pop. 2000 to Now | -5.6% | -14.1% | 15.6% |
| Pop. 1990 to Now | -9.4% | -14.9% | 30.8% |
| space4 | | | |
| Population Density | 1,569.7 | 1,472.7 | 93.4 |
| Land Area | 2.2 | 8.2 | 3,531,905.4 |
| Water Area | 0.1 | 1.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Johnston City, IL | Centralia, IL | United States |
| Age 0 to 4 | 5.0% | 7.6% | 5.9% |
| Age 5 to 9 | 5.9% | 7.0% | 6.1% |
| Age 10 to 14 | 7.0% | 6.9% | 6.6% |
| Age 15 to 17 | 2.2% | 3.1% | 3.9% |
| Age 18 to 20 | 5.2% | 4.8% | 4.0% |
| Age 21 to 24 | 5.4% | 3.2% | 5.2% |
| Age 25 to 34 | 12.7% | 11.8% | 13.8% |
| Age 35 to 44 | 12.9% | 10.6% | 12.9% |
| Age 45 to 54 | 13.3% | 8.8% | 12.6% |
| Age 55 to 59 | 7.8% | 6.7% | 6.7% |
| Age 60 to 64 | 6.8% | 7.3% | 6.3% |
| Age 65 to 74 | 9.0% | 10.8% | 9.6% |
| Age 75 to 84 | 3.3% | 7.1% | 4.5% |
| Age 85 and over | 3.5% | 4.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Johnston City, IL | Centralia, IL | United States |
| White | 97.3% | 81.2% | 59.4% |
| Black | 0.0% | 8.7% | 12.2% |
| Asian | 0.0% | 1.4% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 2.2% | 4.1% | 3.2% |
| Hispanic | 0.5% | 4.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Johnston City, IL | Centralia, IL | United States |
| Married Population | 42.1% | 43.0% | 49.8% |
| Currently Married | 38.7% | 39.9% | 48.0% |
| Married but Separated | 3.4% | 3.2% | 1.8% |
| Single Population | 57.9% | 57.0% | 50.2% |
| Never Married | 30.1% | 32.1% | 33.8% |
| Divorced | 19.3% | 15.5% | 10.8% |
| Widowed | 8.4% | 9.3% | 5.6% |
| space5 | | | |
| Household Size | 2.57 | 2.29 | 2.60 |
| Households | 1,321 | 5,080 | 124,010,992 |
| Family Households | 982 | 2,510 | 80,755,759 |
| Married couple, w/children | 26.1% | 25.5% | 30.5% |
| Married couple, no children | 26.1% | 46.5% | 42.9% |
| Non Family Households | 339 | 2,570 | 43,255,233 |
| Single householder, w/children | 14.6% | 23.3% | 15.8% |
| Single householder, no children | 33.3% | 4.7% | 10.8% |