Derby, CT has a population of 12,755 and is the 3,257th largest city in the United States. The population density is 2,523 per sq mi which is 290% higher than the Connecticut average and 2685% higher than the national average. The median age in Derby is 39 which is approximately 4% lower than the Connecticut average of 41. In Derby, 49% of the population over 15 years of age are married, 72% speak English and 15% speak Spanish. 65% of Derby residents were born in Connecticut, 15% were born out of state, 1% were born outside of the United States and 18% were foreign born.