Plymouth is a town in Litchfield County, Connecticut, United States, located within the Naugatuck Valley Planning Region. It is named after Plymouth, Devon, England. The population was 11,671 at the 2020 census, down from 12,243 at the 2010 census. The town of Plymouth includes the villages of Plymouth Center, Terryville and Pequabuck.

Litchfield County is in northwestern Connecticut, United States. As of the 2020 census, the population was 185,186. The county was named after Lichfield, in England. Litchfield County has the lowest population density of any county in Connecticut and is the state's largest county by area.