Winthrop, WA has a population of 385 and is the 21,090th largest city in the United States. The population density is 414 per sq mi which is 328% higher than the Washington average and 357% higher than the national average. The median age in Winthrop is 40 which is approximately 6% higher than the Washington average of 38. In Winthrop, 55% of the population over 15 years of age are married, 80% speak English and 18% speak Spanish. 40% of Winthrop residents were born in Washington, 40% were born out of state, 2% were born outside of the United States and 18% were foreign born.