It happened at about 1:30 a.m. on the Saugatuck River Bridge.
Police arrived to find a jackknifed tractor trailer blocking two lanes of the highway with five other cars involved in the crash.
10 people were taken to Norwalk Hospital with non-life threatening injuries, and authorities say no one had to be extricated from their cars.
Nine other people refused medical treatment on the scene and were released by EMS.
Connecticut State Police are investigating the cause of the accident.