Winthrop, IA has a population of 915 and is the 15,695th largest city in the United States. The population density is 1,085 per sq mi which is 1887% higher than the Iowa average and 1098% higher than the national average. The median age in Winthrop is 40 which is approximately 6% higher than the Iowa average of 38. In Winthrop, 65% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 90% of Winthrop residents were born in Iowa, 8% were born out of state, 2% were born outside of the United States and 0% were foreign born.