Derby, CT has a population of 12,837 and is the 3,206th largest city in the United States. The population density is 2,539 per sq mi which is 244% higher than the Connecticut average and 2703% higher than the national average. The median age in Derby is 41 which is approximately 3% higher than the Connecticut average of 40. In Derby, 51% of the population over 15 years of age are married, 73% speak English and 15% speak Spanish. 66% of Derby residents were born in Connecticut, 13% were born out of state, 2% were born outside of the United States and 19% were foreign born.