Washington, IA has a population of 7,368 and is the 4,998th largest city in the United States. The population density is 1,405 per sq mi which is 2472% higher than the Iowa average and 1451% higher than the national average. The median age in Washington is 43 which is approximately 14% higher than the Iowa average of 38. In Washington, 59% of the population over 15 years of age are married, 92% speak English and 6% speak Spanish. 73% of Washington residents were born in Iowa, 22% were born out of state, 1% were born outside of the United States and 4% were foreign born.