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.