| | Index, WA | Ilwaco, WA | United States |
| Population | 156 | 1,725 | 329,725,481 |
| Female Population | 50.6% | 49.5% | 50.5% |
| Male Population | 49.4% | 50.5% | 49.5% |
| Median Age | 49.5 | 38.4 | 38.4 |
| space3 | | | |
| Population - 2010 | 176 | 933 | 309,327,143 |
| Population - 2000 | 157 | 950 | 285,036,114 |
| Population - 1990 | 139 | 815 | 251,960,433 |
| Pop. 2000 to Now | 36.3% | 5.9% | 15.6% |
| Pop. 1990 to Now | 54.0% | 23.4% | 30.8% |
| space4 | | | |
| Population Density | 757.3 | 832.9 | 93.4 |
| Land Area | 0.2 | 2.1 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Index, WA | Ilwaco, WA | United States |
| Age 0 to 4 | 0.0% | 6.0% | 5.9% |
| Age 5 to 9 | 3.8% | 6.0% | 6.1% |
| Age 10 to 14 | 7.1% | 5.1% | 6.6% |
| Age 15 to 17 | 2.6% | 1.2% | 3.9% |
| Age 18 to 20 | 0.0% | 0.3% | 4.0% |
| Age 21 to 24 | 3.2% | 4.4% | 5.2% |
| Age 25 to 34 | 6.4% | 24.6% | 13.8% |
| Age 35 to 44 | 13.5% | 5.7% | 12.9% |
| Age 45 to 54 | 19.2% | 9.8% | 12.6% |
| Age 55 to 59 | 11.5% | 4.5% | 6.7% |
| Age 60 to 64 | 11.5% | 6.1% | 6.3% |
| Age 65 to 74 | 10.3% | 17.3% | 9.6% |
| Age 75 to 84 | 8.3% | 6.0% | 4.5% |
| Age 85 and over | 2.6% | 3.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Index, WA | Ilwaco, WA | United States |
| White | 96.2% | 83.5% | 59.4% |
| Black | 0.0% | 0.0% | 12.2% |
| Asian | 3.8% | 0.0% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.2% | 0.2% |
| Other | 0.0% | 0.9% | 0.4% |
| Two or More Races | 0.0% | 5.9% | 3.2% |
| Hispanic | 0.0% | 9.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Index, WA | Ilwaco, WA | United States |
| Married Population | 47.5% | 49.8% | 49.8% |
| Currently Married | 47.5% | 48.5% | 48.0% |
| Married but Separated | 0.0% | 1.3% | 1.8% |
| Single Population | 52.5% | 50.2% | 50.2% |
| Never Married | 23.7% | 31.6% | 33.8% |
| Divorced | 22.3% | 13.9% | 10.8% |
| Widowed | 6.5% | 4.7% | 5.6% |
| space5 | | | |
| Household Size | 2.20 | 3.53 | 2.60 |
| Households | 71 | 487 | 124,010,992 |
| Family Households | 38 | 371 | 80,755,759 |
| Married couple, w/children | 31.6% | 16.2% | 30.5% |
| Married couple, no children | 44.7% | 49.6% | 42.9% |
| Non Family Households | 33 | 116 | 43,255,233 |
| Single householder, w/children | 0.0% | 28.3% | 15.8% |
| Single householder, no children | 23.7% | 5.9% | 10.8% |