Ansonia is a city in New Haven County, Connecticut, United States. Located on the Naugatuck River, it is immediately north of Derby, and about 12 miles (19 km) northwest of New Haven. The population was 18,918 at the time of the 2020 census. The ZIP code for Ansonia is 06401. The city is served by the Metro-North Railroad. Ansonia Station is a stop on the railroad passenger commuter service’s Waterbury Branch connecting to New York’s Grand Central Terminal. Ansonia also is served by the Connecticut Transit bus carrier. Connecticut Route 8 serves Ansonia (Northbound, Exit 18; Southbound, Exit 19).

Ansonia, also referred to as “The Copper City”, is recognized for its history of heavy machine manufacturing industry in the lower Naugatuck Valley. Production included copper, brass, rubber and plastics processing, molding and tubing, iron castings, sheet metal, electric, automatic screw machine, textiles, and foundry products. The well-known Ansonia Clock Company was founded here in 1851.

Ansonia is the birthplace of David Humphreys, a diplomat and colonel in the American Revolutionary War.

The area along the Naugatuck River, comprising the present Elm Street section of Ansonia and Derby Avenue section of Derby, was first settled by English colonists in 1652; it was originally a part of the township of Derby. Early settlers developed subsistence farming, and used the river for sawmills and gristmills.

In 1844, Anson Green Phelps (1781–1853), a merchant and philanthropist, wanted to expand the old borough of Birmingham (the present downtown of the city of Derby) to the north along the west side of the Naugatuck River to enable industrial development. Unable to purchase the land from its owner, in 1844 Phelps acquired land along the east side of the river; today this is Ansonia’s downtown section. A canal was dug for river power to drive the factories and businesses in the new industrial village, which Phelps named “Ansonia”. He wanted to name the industrial village as “Phelpsville”, but learned there was another village in the region by that name. As suggested by a friend, Phelps changed his first name to create the name “Ansonia”.

As industry developed, soon Ansonia became the most populous area of Derby, boasting many factories. The state chartered Ansonia as a borough of Derby in 1864 and amended it in 1871, granting full municipal privileges. In 1888, a petition was circulated in the borough of Ansonia for the purpose of becoming a separate township from Derby. In 1889 the State General Assembly granted the separation, constituting the Borough, Hilltop, West Ansonia, and Elm Street areas as a separate town known as Ansonia. This was the 168th township in the state of Connecticut. In 1893, Ansonia was incorporated as a city, consolidating with the coterminous Town and the old borough.