Naugatuck is a consolidated borough and town in New Haven County, Connecticut, United States. The town, part of the Naugatuck Valley Planning Region, had a population of 31,519 as of the 2020 Census. The town spans both sides of the Naugatuck River just south of Waterbury and includes the communities of Union City on the east side of the river, …Naugatuck is a consolidated borough and town in New Haven County, Connecticut, United States. The town, part of the Naugatuck Valley Planning Region, had a population of 31,519 as of the 2020 Census. The town spans both sides of the Naugatuck River just south of Waterbury and includes the communities of Union City on the east side of the river, Straitsville on the southeast, and Millville on the west.