Oso, WA has a population of 293 and is the 22,622nd largest city in the United States. The population density is 104 per sq mi which is 8% higher than the Washington average and 15% higher than the national average. The median age in Oso is 44 which is approximately 17% higher than the Washington average of 38. In Oso, 65% of the population over 15 years of age are married, 100% speak English and 0% speak Spanish. 56% of Oso residents were born in Washington, 39% were born out of state, 2% were born outside of the United States and 3% were foreign born.