Groton, CT has a population of 9,240 and is the 4,171st largest city in the United States. The population density is 2,997 per sq mi which is 363% higher than the Connecticut average and 3208% higher than the national average. The median age in Groton is 34 which is approximately 16% lower than the Connecticut average of 41. In Groton, 42% of the population over 15 years of age are married, 83% speak English and 9% speak Spanish. 49% of Groton residents were born in Connecticut, 38% were born out of state, 3% were born outside of the United States and 10% were foreign born.