| | Westfield, IN | Zionsville, IN | United States |
| Population | 45,695 | 30,258 | 329,725,481 |
| Female Population | 51.5% | 49.5% | 50.5% |
| Male Population | 48.5% | 50.5% | 49.5% |
| Median Age | 36.5 | 41.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 30,249 | 24,494 | 309,327,143 |
| Population - 2000 | 9,293 | 8,775 | 285,036,114 |
| Population - 1990 | 3,304 | 5,281 | 251,960,433 |
| Pop. 2000 to Now | 396.6% | 234.4% | 15.6% |
| Pop. 1990 to Now | 1,296.6% | 455.6% | 30.8% |
| space4 | | | |
| Population Density | 1,503.5 | 565.5 | 93.4 |
| Land Area | 30.4 | 53.5 | 3,531,905.4 |
| Water Area | 0.2 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Westfield, IN | Zionsville, IN | United States |
| Age 0 to 4 | 6.6% | 5.4% | 5.9% |
| Age 5 to 9 | 9.9% | 8.4% | 6.1% |
| Age 10 to 14 | 8.7% | 7.8% | 6.6% |
| Age 15 to 17 | 3.6% | 5.4% | 3.9% |
| Age 18 to 20 | 3.0% | 2.5% | 4.0% |
| Age 21 to 24 | 3.6% | 3.7% | 5.2% |
| Age 25 to 34 | 12.2% | 7.6% | 13.8% |
| Age 35 to 44 | 16.1% | 14.6% | 12.9% |
| Age 45 to 54 | 13.7% | 17.9% | 12.6% |
| Age 55 to 59 | 5.7% | 7.4% | 6.7% |
| Age 60 to 64 | 4.8% | 6.1% | 6.3% |
| Age 65 to 74 | 7.7% | 7.6% | 9.6% |
| Age 75 to 84 | 2.7% | 3.8% | 4.5% |
| Age 85 and over | 1.7% | 1.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Westfield, IN | Zionsville, IN | United States |
| White | 81.2% | 89.6% | 59.4% |
| Black | 2.7% | 2.0% | 12.2% |
| Asian | 2.7% | 4.2% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.6% | 0.1% | 0.4% |
| Two or More Races | 3.8% | 1.5% | 3.2% |
| Hispanic | 8.9% | 2.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Westfield, IN | Zionsville, IN | United States |
| Married Population | 65.1% | 71.6% | 49.8% |
| Currently Married | 63.9% | 70.9% | 48.0% |
| Married but Separated | 1.2% | 0.7% | 1.8% |
| Single Population | 34.9% | 28.4% | 50.2% |
| Never Married | 21.0% | 20.9% | 33.8% |
| Divorced | 9.6% | 4.5% | 10.8% |
| Widowed | 4.3% | 3.0% | 5.6% |
| space5 | | | |
| Household Size | 2.70 | 2.79 | 2.60 |
| Households | 16,837 | 10,835 | 124,010,992 |
| Family Households | 12,996 | 9,033 | 80,755,759 |
| Married couple, w/children | 42.6% | 43.0% | 30.5% |
| Married couple, no children | 39.6% | 48.3% | 42.9% |
| Non Family Households | 3,841 | 1,802 | 43,255,233 |
| Single householder, w/children | 11.4% | 5.2% | 15.8% |
| Single householder, no children | 6.3% | 3.4% | 10.8% |