Harwinton is a town in Litchfield County, Connecticut, United States. The population was 5,642 at the 2010 census, up from 5,283 at the 2000 census. The high school is Lewis S. Mills.
The town incorporated in 1737. The name of the town alludes to Hartford and Windsor, Connecticut.
Harwinton is in eastern Litchfield County; it is bordered to the northwest by the city of Torrington and to the east by Burlington in Hartford County. Hartford, the state capital, is 23 miles (37 km) to the east, and Bristol is 11 miles (18 km) to the southeast.
According to the United States Census Bureau, the town of Harwinton has a total area of 31.2 square miles (80.7 km2), of which 30.8 square miles (79.8 km2) are land and 0.35 square miles (0.9 km2) of it, or 1.12%, are water. The town is bordered to the west by the Naugatuck River. The southeastern portion of the town contains the Roraback Wildlife Area and several reservoirs.
As of the census of 2000, there were 5,283 people, 1,958 households, and 1,546 families living in the town.