Marion, IA has a population of 37,198 and is the 1,117th largest city in the United States. The population density is 2,114 per sq mi which is 3770% higher than the Iowa average and 2234% higher than the national average. The median age in Marion is 37 which is approximately 2% lower than the Iowa average of 38. In Marion, 62% of the population over 15 years of age are married, 97% speak English and 1% speak Spanish. 74% of Marion residents were born in Iowa, 23% were born out of state, 1% were born outside of the United States and 3% were foreign born.