Cos Cob, CT has a population of 6,535 and is the 5,438th largest city in the United States. The population density is 3,147 per sq mi which is 386% higher than the Connecticut average and 3374% higher than the national average. The median age in Cos Cob is 43 which is approximately 7% higher than the Connecticut average of 41. In Cos Cob, 63% of the population over 15 years of age are married, 71% speak English and 10% speak Spanish. 35% of Cos Cob residents were born in Connecticut, 37% were born out of state, 2% were born outside of the United States and 25% were foreign born.