Denison, IA has a population of 8,326 and is the 4,561st largest city in the United States. The population density is 1,275 per sq mi which is 2233% higher than the Iowa average and 1307% higher than the national average. The median age in Denison is 33 which is approximately 13% lower than the Iowa average of 38. In Denison, 60% of the population over 15 years of age are married, 59% speak English and 38% speak Spanish. 51% of Denison residents were born in Iowa, 26% were born out of state, 0% were born outside of the United States and 22% were foreign born.