ATVs from Vermont, New York, Pennsylvania, and Florida can be driven in Connecticut without a Connecticut registration. All other out-of-state registered ATVs must be registered in Connecticut before it can be used. The owner must present an out-of-state registration, out-of-state operator license, and Application for Snowmobile or All-Terrain Vehicle Registration (form B-77), which can be obtained from a DMV office.
Check out these Sharon, CT ATV/OHV resources:
