| | Willow Creek, CA | Tracy, CA | United States |
| Population | 1,298 | 92,792 | 329,725,481 |
| Female Population | 44.2% | 49.3% | 50.5% |
| Male Population | 55.9% | 50.7% | 49.5% |
| Median Age | 39.3 | 33.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 1,276 | 83,605 | 309,327,143 |
| Population - 2000 | 1,743 | 56,929 | 285,036,114 |
| Population - 1990 | 1,576 | 33,558 | 251,960,433 |
| Pop. 2000 to Now | -17.8% | 66.9% | 15.6% |
| Pop. 1990 to Now | -9.1% | 183.2% | 30.8% |
| space4 | | | |
| Population Density | 42.8 | 4,190.8 | 93.4 |
| Land Area | 30.3 | 22.1 | 3,531,905.4 |
| Water Area | 0.3 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Willow Creek, CA | Tracy, CA | United States |
| Age 0 to 4 | 5.5% | 6.7% | 5.9% |
| Age 5 to 9 | 9.0% | 7.2% | 6.1% |
| Age 10 to 14 | 5.1% | 9.4% | 6.6% |
| Age 15 to 17 | 1.3% | 4.5% | 3.9% |
| Age 18 to 20 | 3.9% | 4.7% | 4.0% |
| Age 21 to 24 | 2.0% | 4.9% | 5.2% |
| Age 25 to 34 | 16.9% | 13.7% | 13.8% |
| Age 35 to 44 | 8.6% | 14.1% | 12.9% |
| Age 45 to 54 | 2.5% | 14.4% | 12.6% |
| Age 55 to 59 | 13.7% | 5.7% | 6.7% |
| Age 60 to 64 | 9.5% | 5.0% | 6.3% |
| Age 65 to 74 | 14.8% | 6.1% | 9.6% |
| Age 75 to 84 | 6.6% | 2.3% | 4.5% |
| Age 85 and over | 0.6% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Willow Creek, CA | Tracy, CA | United States |
| White | 79.4% | 28.0% | 59.4% |
| Black | 0.0% | 4.9% | 12.2% |
| Asian | 0.0% | 18.5% | 5.6% |
| Native American | 4.3% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 4.2% | 1.1% | 0.2% |
| Other | 2.7% | 0.4% | 0.4% |
| Two or More Races | 5.2% | 5.5% | 3.2% |
| Hispanic | 4.2% | 41.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Willow Creek, CA | Tracy, CA | United States |
| Married Population | 59.3% | 53.7% | 49.8% |
| Currently Married | 59.3% | 51.5% | 48.0% |
| Married but Separated | 0.0% | 2.2% | 1.8% |
| Single Population | 40.7% | 46.3% | 50.2% |
| Never Married | 23.2% | 33.0% | 33.8% |
| Divorced | 7.3% | 9.2% | 10.8% |
| Widowed | 10.3% | 4.1% | 5.6% |
| space5 | | | |
| Household Size | 2.32 | 3.40 | 2.60 |
| Households | 559 | 27,237 | 124,010,992 |
| Family Households | 270 | 21,603 | 80,755,759 |
| Married couple, w/children | 44.1% | 42.5% | 30.5% |
| Married couple, no children | 55.9% | 32.6% | 42.9% |
| Non Family Households | 289 | 5,634 | 43,255,233 |
| Single householder, w/children | 0.0% | 13.7% | 15.8% |
| Single householder, no children | 0.0% | 11.2% | 10.8% |