The city of Rome, in New York’s Oneida County, once produced one-tenth of the copper used in the United States. The Rome Brass & Copper Co. advertised that Rome was “The Brass and Copper City” in 1919.
 
Rome’s nickname of ‘Copper City” has been cited in print since at least 1920.
 
   
Wikipedia: Rome, New York
Rome is a city in New York State. It is located in Oneida County, which is in north-central or “Upstate” New York. The population was 33,725 at the 2010 census. Rome is one of two principal cities in the Utica–Rome Metropolitan Statistical Area, which lies in the “Leatherstocking Country” made famous by James Fenimore Cooper’s Leatherstocking Tales, set in frontier days after the American Revolutionary War. Rome is in New York’s 22nd congressional district.
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Copper City
Jesse Williams founded the first cheese factory in the United States at Rome in 1851. Williams also developed the process used today for large-scale cheese manufacturing. There were numerous dairy farms in the area and throughout the Mohawk Valley.
 
The City of Rome was incorporated in 1870.
 
Revere Copper Products, Inc., founded in Rome between 1928 and 1929, is one of the oldest manufacturing companies in the United States.
       
NYS Historic Newspapers 
17 September 1919, Fulton (NY) Patriot, pg. 11, col. 5 ad:
ROME BRASS & COPPER CO.
ROME, N. Y.
(The Brass and Copper City)
 
NYS Historic Newspapers
19 April 1920, Ogdensburg (NY) Republican-Journal, “The State Trooper,” pg. 4, col. 2:
Those who are familiar with Rome, know of the diversified population of the Copper City.
 
22 November 1923, New York (NY) Times, “Our Debt to Rome, N. Y.,“pg. 18, col. 6:
To the Editor of The New York Times:
In THE TIMES of Sunday, Nov. 18, was an article entitled “It Is a Mighty Mean City That Boasts No Nickname,” which I read anticipating that you were telling the world that Rome, N. Y., was known as “The Copper City,” because more than one-tenth of the copper used in the United States was manufactured in Rome. Not that we thought that the world didn’t know it. We believed it did.
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ROME CHAMBER OF COMMERCE
E. D. BEVITT, Secretary.
 
However, as the gentleman who wrote the article did not know it or forgot it, we hasten to tell him, or remind him, as the case may be.
ROME CHAMBER OF COMMERCE
E. D. BEVITT, Secretary,
Rome, Nov. 20, 1923.
 
Google Books   
History of the Mohawk Valley, Gateway to the West, 1614-1925:
Covering the six counties of Schenectady, Schoharie, Montgomery, Fulton, Herkimer, and Oneida, Volume 2
Edited by Nelson Greene
CHicago, IL: S. J. Clarke
1925
Pg. 1880:
THE CITY OF ROME.
BY E. D. BEVITT
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Another Rip Van Winkle, awakening in Rome in 1925, would find several things to excite his wonder in addition to the changes incident to the growth of over 60 per cent, which the city experienced in the first twenty years of the present century. Informed that twenty years had passed since his last waking hours, he might visualize a city of 28,000 people with a corresponding increase in the size and number of its varied industries but he would not expect to find “The Copper City” ...
 
1 April 1930, New York (NY) Times, pg. 22, col. 1 ad:
General Motors Truck Company
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ROME—Copper City Motors
 
20 March 1939, Syracuse (NY) Journal, pg. C5, col. 1:
Flag First Flew In Battle at Rome
Community Sprang From Old “Carrying Place”; Rich in History; Great Copper City of Nation
BY J. WALTER SCHEID
 
OCLC WorldCat record
A map and street guide, Rome, N.Y. : the Copper City.
Author: Rome Chamber of Commerce (N.Y.). Public Relations Committee.
Publisher: [Rome, N.Y.] : Rome Chamber of Commerce, Public Relations Committee, [1951?]
Edition/Format:   Map : English
 
OCLC WorldCat record
Industrial Main Street; the story of Rome, the copper city.
Author: Isaac Frederick Marcosson
Publisher: New York, Dodd, Mead, 1953.
Edition/Format:   Print book : English
 
Google Books
Rome
By Portia Vescio, Rome Historical Society (Rome, N.Y.)
Portsmouth, NH: Arcadia
2004
Pg. 8:
This large corporation, famous for Revere Ware pots and pans and its Art Deco pieces of the 1930s, helped make Rome known as “the Copper City.” In its heyday before World War II, one-tenth of copper in this country was produced in Rome, ..resulting in spin-off companies such as the Rome-Turner Radiator Company.