Derby, IA has a population of 133 and is the 26,091st largest city in the United States. The population density is 511 per sq mi which is 836% higher than the Iowa average and 464% higher than the national average. The median age in Derby is 41 which is approximately 8% higher than the Iowa average of 38. In Derby, 63% of the population over 15 years of age are married, 93% speak English and 1% speak Spanish. 80% of Derby residents were born in Iowa, 20% were born out of state, 0% were born outside of the United States and 0% were foreign born.