The nickname “Second City of the World” (or “Second City in the World”) was popularized with the 1898 consolidation of Manhattan, Brooklyn and other areas into Greater New York. New York City (with about 3,200,000 people in 1898) became second in population in the world to London (with about 5,000,000 people).
 
Consolidation proposals in the 1880s used the “Second City” term. “The New York Herald says the time has come to do away with the two cities of New York and Brooklyn and the merging of them into one great metropolis, the second city of the world in population and commercial importance” was cited in an 1885 newspaper. “Second city of the world” was used in 1890 by Andrew H. Green (1820-1903), the president of a commission to explore the consolidation.
 
Both “Second City in the World” and “Second City of the World” were used by newspapers in May 1891, when the 1890 census indicated that a greater New York would be the second most populous city in the world. “The Second City of the World” was the title of an article in The Peterson Magazine (Philadelphia, PA) in October 1896.
 
New York City would become the most populous city in the world by 1925, but it would lose that title to Tokyo in 1965. The “Second City of the World” nickname is of historical interest today.
 
       
20 November 1885, Duluth (MN) Tribune, pg. 1, col. 5:
The New York Herald says the time has come to do away with the two cities of New York and Brooklyn and the merging of them into one great metropolis, the second city of the world in population and commercial importance, and also, if it is thought advisable, of obliterating both names and adopting the common name of Manhattan.
   
5 August 1886, Daily Nebraska State Journal (Lincoln, NE), pg. 4, col. 3:
The board of aldermen of New York have under consideration the big scheme of the consolidation of New York, Brooklyn, Long Island City and other neighboring towns and villages into one great city to be known as “Manhattan,” containing a population of 2,500,000 people and ranking as the second city of the world in wealth and population. The project was originally proposed by the New York Star, and is met with favor by Brooklyn and the others from the fact shown that there would be a reduction in taxes.
 
7 June 1890, Watertown (NY) Daily Times, pg. 4, col. 2:
THE GREATER NEW YORK.
In his address as president of the commission to inquire into the expediency of consolidating the communities about the port of New York into one great municipality, Mr. Andrew H. Green pointed out that together they would make up the second city of the world as to size. London alone contains a great population.
 
These communities comprise four cities of independent municipal governments, and are situated in two states and four counties. Their combined population at present exceeds 3,000,000. The population of London is about 4,275,000, and in 1886 Paris contained not less than 2,350,000.
 
21 May 1891, Christian Union (New York, NY), pg. 683, col. 3:
SECOND CITY IN THE WORLD.
The census of 1890 proves that within a radius of fifteen miles from the center of the city of New York there is a population considerably in excess of 3,000,000 people, or more than two-thirds that of the city of London.
 
23 May 1891, The Daily American (Nashville, TN), pg. 3, col. 1:
Second City of the World.
The census of 1890 proves that within a radius of fifteen miles from the centre of the city of New York there is a population considerably in excess of 3,000,000 people, or more than two-thirds that of the city of London.
   
1 March 1894, The Sun (Baltimore, MD), pg. 6, col. 8:
TOPICS IN NEW YORK.
Governor Flower Signs the City Consolidation Bill
PEOPLE TO VOTE ON THE QUESTION
If Adopted New York Will Have 3,000,000 Population and Be the Second City of the World
(...)
The project if carried through will make a city with an area of about 125 square miles and a population of about 3,000,000 souls. It will be second only to London in the cities of the world.
 
October 1896, The Peterson Magazine (Philadelphia, PA), pg. 1:
THE SECOND CITY OF THE WORLD.
IN fifteen months more Greater New York will be a reality, unless the wheels of progress are unexpectedly blocked.
 
Chronicling America
15 May 1897, The Irish Standard (Minneapolis, MN), pg. 4, col. 7:
The municipality of the Greater New York will begin its official existence on Jan. 1, 1898, under the government of a Mayor and Municipal Assembly to be elected by the people on the first day of next November. The population of the new city, which will be known under the corporate name of “The City of New York,” will be about 3,500,000, making it rank as the second city in the world, London being the first.
   
Chronicling America
13 May 1897, The Bee (Earlington, KY), pg. 2, col. 1:
“GREATER New York” will have a population of more than 3,000,000, and will be the second city in the world.
 
Chronicling America
19 May 1897, The Anderson Intelligencer (Anderson Court House, SC), pg. 2, col. 1:
It is now Greater New York. When Governor Black signed the charter, the second city of the world sprang into being. The official existence of this giant city will begin January 1, 1898.
     
23 May 1897, Detroit (MI) Free Press, pg. 20, col. 3:
SECOND CITY OF THE WORLD.
THE PROUD DISTINCTION CLAIMED BY GREATER NEW YORK.
A DESCRIPTIVE VIEW OF THE ENLARGED METROPOLIS.
The City Divided Into Five Under One Administration.
   
2 January 1898, The Sun (New York, NY), pg. 3, col. 1:
OUR IMPERIAL CITY.
Varied Wonders Presented by the New New York.
ITS GREATNESS AND WEALTH
Interesting Facts Concerning the Second City in the World.
 
OCLC WorldCat record
A volume commemorating the creation of the second city of the world by the consolidation of the communities adjacent to New York Harbor under the new charter of the city of New York.
Author: Edward Hagaman Hall
Publisher: New York : The Republic Press, 1898.
Series: Genealogy & local history, LH5525.
Edition/Format:   Book   Microform : Microfilm : Master microform : English
 
Google Books
The New Encyclopedic Atlas and Gazetteer of the World
New York, NY: P. F. Collier & Son
1907
Pg. 265:
As a business centre New York has long been not only the first city of this continent, but the second city of the world, London being its only superior.
 
Chronicling America
22 January 1910, Superior (WI) Times, “Little Old New York” by James Creelman, pg. 8, col. 1:
But New York, the second city of the world, is not American. It is the only cosmopolis in existence. With a population of 4,000,000 inhabitants, it has nearly 2,000,000 who were born in foreign countries.