Darien, CT has a population of 21,519 and is the 2,017th largest city in the United States. The population density is 1,701 per sq mi which is 163% higher than the Connecticut average and 1777% higher than the national average. The median age in Darien is 39 which is approximately 4% lower than the Connecticut average of 41. In Darien, 70% of the population over 15 years of age are married, 87% speak English and 4% speak Spanish. 38% of Darien residents were born in Connecticut, 50% were born out of state, 2% were born outside of the United States and 11% were foreign born.