| | Arlington, WA | Spanaway, WA | United States |
| Population | 19,832 | 34,670 | 329,725,481 |
| Female Population | 50.9% | 49.2% | 50.5% |
| Male Population | 49.1% | 50.9% | 49.5% |
| Median Age | 39.2 | 31.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 17,987 | 28,054 | 309,327,143 |
| Population - 2000 | 11,713 | 21,588 | 285,036,114 |
| Population - 1990 | 4,037 | 15,001 | 251,960,433 |
| Pop. 2000 to Now | 79.9% | 53.1% | 15.6% |
| Pop. 1990 to Now | 421.9% | 120.3% | 30.8% |
| space4 | | | |
| Population Density | 2,023.5 | 3,954.6 | 93.4 |
| Land Area | 9.8 | 8.8 | 3,531,905.4 |
| Water Area | 0.0 | 0.4 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Arlington, WA | Spanaway, WA | United States |
| Age 0 to 4 | 5.9% | 6.7% | 5.9% |
| Age 5 to 9 | 6.0% | 8.5% | 6.1% |
| Age 10 to 14 | 7.7% | 8.1% | 6.6% |
| Age 15 to 17 | 3.9% | 5.7% | 3.9% |
| Age 18 to 20 | 3.2% | 3.5% | 4.0% |
| Age 21 to 24 | 4.5% | 4.9% | 5.2% |
| Age 25 to 34 | 11.4% | 17.5% | 13.8% |
| Age 35 to 44 | 16.7% | 13.6% | 12.9% |
| Age 45 to 54 | 14.7% | 11.3% | 12.6% |
| Age 55 to 59 | 5.7% | 6.7% | 6.7% |
| Age 60 to 64 | 7.7% | 4.0% | 6.3% |
| Age 65 to 74 | 7.2% | 6.2% | 9.6% |
| Age 75 to 84 | 3.5% | 2.6% | 4.5% |
| Age 85 and over | 2.1% | 0.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Arlington, WA | Spanaway, WA | United States |
| White | 71.4% | 52.2% | 59.4% |
| Black | 1.6% | 9.3% | 12.2% |
| Asian | 5.6% | 6.6% | 5.6% |
| Native American | 0.7% | 0.9% | 0.6% |
| Hawaiian, Pacific Islander | 0.5% | 5.3% | 0.2% |
| Other | 0.4% | 0.3% | 0.4% |
| Two or More Races | 5.9% | 11.0% | 3.2% |
| Hispanic | 14.0% | 14.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Arlington, WA | Spanaway, WA | United States |
| Married Population | 56.8% | 51.3% | 49.8% |
| Currently Married | 54.8% | 49.4% | 48.0% |
| Married but Separated | 2.0% | 1.8% | 1.8% |
| Single Population | 43.2% | 48.7% | 50.2% |
| Never Married | 24.5% | 32.4% | 33.8% |
| Divorced | 12.6% | 13.6% | 10.8% |
| Widowed | 6.2% | 2.7% | 5.6% |
| space5 | | | |
| Household Size | 2.64 | 3.06 | 2.60 |
| Households | 7,493 | 11,304 | 124,010,992 |
| Family Households | 5,168 | 8,466 | 80,755,759 |
| Married couple, w/children | 38.7% | 33.8% | 30.5% |
| Married couple, no children | 42.0% | 34.8% | 42.9% |
| Non Family Households | 2,325 | 2,838 | 43,255,233 |
| Single householder, w/children | 11.1% | 20.4% | 15.8% |
| Single householder, no children | 8.2% | 11.0% | 10.8% |