Onawa, IA has a population of 2,906 and is the 8,968th largest city in the United States. The population density is 560 per sq mi which is 925% higher than the Iowa average and 518% higher than the national average. The median age in Onawa is 42 which is approximately 9% higher than the Iowa average of 38. In Onawa, 57% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 71% of Onawa residents were born in Iowa, 28% were born out of state, 0% were born outside of the United States and 1% were foreign born.