Winthrop is a hamlet and census-designated place (CDP) in the town of Stockholm in St. Lawrence County, New York, United States.

The community is in northeastern St. Lawrence County, in the northeastern part of the town of Stockholm.

New York State Route 11C passes through Winthrop, leading southwest 3 miles (5 km) to U.S. Route 11 at Stockholm Center, and looping northeast, east, and south 8 miles (13 km) to rejoin Route 11 at Cotey Corners in the town of Lawrence.

The village of Potsdam is 13 miles (21 km) southwest of Winthrop.

State Route 420 crosses NY 11C in the center of Winthrop; it leads north-northwest 11 miles (18 km) to Massena and south 1.5 miles (2.4 km) to US-11.