Ansonia - The Copper City[3]
Berlin – Geographic Center of Connecticut[4]
Bethlehem – The Christmas Town[5]
Bridgeport – The Park City[6]
Bristol-Clock City[6]
Cheshire – Bedding Plant Capital of Connecticut.[8]
Danbury – Hat City.[6][9]
Derby – Connecticut's Smallest City[10]
East Hampton – Belltown USA[11]
Groton – Submarine Capital of the World[12][13]
Hamden – Land of the Sleeping Giant[14]
Hartford-Insurance Capital of the World[15]
Manchester – Silk City[6]
Meriden – Silver City[6]
Middletown – Forest City[17]
Naugatuck – Rubber City[6]
New Britain-Hardware City[6][16]
New Haven – The Elm City[6][19] (reported in the 1880s as City of Elms[20])
Norwich – Rose City[21] or The Rose of New England[22]
Stamford-Lock City (a reference to the now-defunct Yale & Towne lock factory).[16]
Waterbury – The Brass City[6][24]
West Haven – Connecticut's Friendliest City[25]
Willimantic – Thread City[6]
Winsted – Laurel City[26]

From wiki but I'm too lazy to take out the citations.