Decorah, IA has a population of 7,985 and is the 4,688th largest city in the United States. The population density is 1,122 per sq mi which is 1954% higher than the Iowa average and 1139% higher than the national average. The median age in Decorah is 31 which is approximately 18% lower than the Iowa average of 38. In Decorah, 46% of the population over 15 years of age are married, 97% speak English and 2% speak Spanish. 54% of Decorah residents were born in Iowa, 44% were born out of state, 0% were born outside of the United States and 3% were foreign born.