| | Gas City, IN | Marion, IN | United States |
| Population | 6,088 | 27,757 | 329,725,481 |
| Female Population | 53.3% | 54.0% | 50.5% |
| Male Population | 46.7% | 46.0% | 49.5% |
| Median Age | 40.5 | 36.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 6,134 | 29,824 | 309,327,143 |
| Population - 2000 | 5,940 | 31,320 | 285,036,114 |
| Population - 1990 | 6,296 | 32,618 | 251,960,433 |
| Pop. 2000 to Now | -4.1% | -11.6% | 15.6% |
| Pop. 1990 to Now | -9.5% | -15.2% | 30.8% |
| space4 | | | |
| Population Density | 1,345.7 | 1,781.0 | 93.4 |
| Land Area | 4.5 | 15.6 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Gas City, IN | Marion, IN | United States |
| Age 0 to 4 | 5.9% | 5.1% | 5.9% |
| Age 5 to 9 | 7.5% | 4.5% | 6.1% |
| Age 10 to 14 | 5.1% | 6.5% | 6.6% |
| Age 15 to 17 | 6.5% | 2.9% | 3.9% |
| Age 18 to 20 | 3.9% | 8.9% | 4.0% |
| Age 21 to 24 | 1.7% | 9.4% | 5.2% |
| Age 25 to 34 | 10.9% | 11.6% | 13.8% |
| Age 35 to 44 | 12.8% | 8.4% | 12.9% |
| Age 45 to 54 | 12.9% | 10.0% | 12.6% |
| Age 55 to 59 | 6.5% | 6.9% | 6.7% |
| Age 60 to 64 | 5.3% | 6.8% | 6.3% |
| Age 65 to 74 | 9.4% | 10.5% | 9.6% |
| Age 75 to 84 | 5.5% | 5.6% | 4.5% |
| Age 85 and over | 6.0% | 2.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Gas City, IN | Marion, IN | United States |
| White | 94.7% | 73.0% | 59.4% |
| Black | 2.0% | 13.9% | 12.2% |
| Asian | 1.9% | 1.1% | 5.6% |
| Native American | 0.0% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 1.0% | 4.7% | 3.2% |
| Hispanic | 0.5% | 7.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Gas City, IN | Marion, IN | United States |
| Married Population | 51.3% | 31.7% | 49.8% |
| Currently Married | 49.7% | 30.6% | 48.0% |
| Married but Separated | 1.6% | 1.1% | 1.8% |
| Single Population | 48.7% | 68.3% | 50.2% |
| Never Married | 28.7% | 41.1% | 33.8% |
| Divorced | 11.6% | 19.5% | 10.8% |
| Widowed | 8.4% | 7.6% | 5.6% |
| space5 | | | |
| Household Size | 2.41 | 2.18 | 2.60 |
| Households | 2,498 | 10,806 | 124,010,992 |
| Family Households | 1,729 | 5,848 | 80,755,759 |
| Married couple, w/children | 29.3% | 19.6% | 30.5% |
| Married couple, no children | 37.9% | 36.9% | 42.9% |
| Non Family Households | 769 | 4,958 | 43,255,233 |
| Single householder, w/children | 24.8% | 30.3% | 15.8% |
| Single householder, no children | 7.9% | 13.2% | 10.8% |