Charter Oak, IA has a population of 596 and is the 18,485th largest city in the United States. The population density is 1,235 per sq mi which is 2160% higher than the Iowa average and 1263% higher than the national average. The median age in Charter Oak is 40 which is approximately 6% higher than the Iowa average of 38. In Charter Oak, 69% of the population over 15 years of age are married, 89% speak English and 10% speak Spanish. 75% of Charter Oak residents were born in Iowa, 20% were born out of state, 1% were born outside of the United States and 5% were foreign born.