Arlington, WA has a population of 18,749 and is the 2,329th largest city in the United States. The population density is 1,913 per sq mi which is 1879% higher than the Washington average and 2011% higher than the national average. The median age in Arlington is 37 which is approximately 1% lower than the Washington average of 38. In Arlington, 62% of the population over 15 years of age are married, 91% speak English and 4% speak Spanish. 60% of Arlington residents were born in Washington, 33% were born out of state, 1% were born outside of the United States and 6% were foreign born.