Riverdale, IA has a population of 481 and is the 19,776th largest city in the United States. The population density is 262 per sq mi which is 380% higher than the Iowa average and 189% higher than the national average. The median age in Riverdale is 45 which is approximately 18% higher than the Iowa average of 38. In Riverdale, 67% of the population over 15 years of age are married, 93% speak English and 7% speak Spanish. 62% of Riverdale residents were born in Iowa, 36% were born out of state, 0% were born outside of the United States and 2% were foreign born.