Ottumwa, IA has a population of 24,709 and is the 1,762nd largest city in the United States. The population density is 1,558 per sq mi which is 2752% higher than the Iowa average and 1620% higher than the national average. The median age in Ottumwa is 36 which is approximately 4% lower than the Iowa average of 38. In Ottumwa, 57% of the population over 15 years of age are married, 83% speak English and 13% speak Spanish. 70% of Ottumwa residents were born in Iowa, 19% were born out of state, 1% were born outside of the United States and 11% were foreign born.