Naugatuck is a consolidated borough and town in New Haven County, Connecticut, United States. 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, which has its own post office, Straitsville on the southeast, and Millville on the west. As of the 2010 census, Naugatuck had a population of 31,862.