Santiago, WA has a population of 18 and is the 28,821st largest city in the United States. The population density is 11 per sq mi which is 88% lower than the Washington average and 87% lower than the national average. The median age in Santiago is 33 which is approximately 14% lower than the Washington average of 38. In Santiago, 20% of the population over 15 years of age are married, 100% speak English and 0% speak Spanish. 44% of Santiago residents were born in Washington, 56% were born out of state, 0% were born outside of the United States and 0% were foreign born.