“North New York” is a 19th century name for what is now the South Bronx (Mott Haven and Port Morris). The Evening Post (New York, NY) stated on November 10, 1868:
 
“Passing over the Harlem bridge at the end of Third avenue, the district of Mott Haven is found on the left, and that of North New York on the right. Both extend to One Hundred and Thirty-Eighth street. North New York extends easterly five blocks to St. Ann’s avenue.”
   
The name “North New York” largely disappeared after 1898 (when the Bronx was made a borough of New York City), but the name reappeared by 2010 and began to be featured in real estate listings. “Apparently there’s a north new york in the south bronx, east new york in brooklyn, and west new york in jersey… Can’t find a south ny tho” was posted on Twitter on January 14, 2011.
 
   
Wikipedia: South Bronx
The South Bronx is an area of the New York City borough of the Bronx. As the name implies, the area comprises neighborhoods in the southern part of the Bronx, such as Mott Haven, Melrose, and Port Morris. Formerly a deteriorating, poverty-stricken area, the South Bronx is now known for its hip-hop culture and its graffiti.
 
Wikipedia: Mott Haven, Bronx
Mott Haven is a primarily residential neighborhood in the southwestern section of the Bronx borough in New York City. Zip codes include 10451, 10454, and 10455. The neighborhood is part of Bronx Community Board 1. Its boundaries, starting from the north and moving clockwise, are East 149th Street to the north, the Bruckner Expressway to the east, the Bronx Kill waterway to the south, and the Harlem River to the west.
(...)
Mott Haven and Port Morris were the first neighborhoods to give rise to the term “South Bronx”. Together, they were earlier known as the North Side or North New York.
 
Wikipedia: Port Morris, Bronx
Port Morris is a mixed use, primarily industrial neighborhood geographically located in the southwest Bronx, New York City. The neighborhood is part of Bronx Community Board 1. Its boundaries are the Major Deegan Expressway and Bruckner Expressway to the north, East 149th Street to the east, the East River to the southeast, the Bronx Kill south, and the Harlem River to the west. Its ZIP code is 10454. The neighborhood is served by the NYPD’s 40th Precinct.
 
10 November 1868, The Evening Post (New York, NY), pg. 2, col. 2:
Port Morris.
Passing over the Harlem bridge at the end of Third avenue, the district of Mott Haven is found on the left, and that of North New York on the right. Both extend to One Hundred and Thirty-Eighth street. North New York extends easterly five blocks to St. Ann’s avenue.
     
24 June 1874, The Daily Graphic (New York, NY), “Up-town Postal Facilities,” pg. 874, col. 3:
The letters will be delivered by carriers throughout this district, which comprises the old town of Morrisania, and the little settlements known as Mott Haven, North New York-Milton, Melrose, Port Morris, &c.
 
Google Books
Library of Universal Knowledge
Volume 10
New York, NY: American Book Exchange
1881
Pg. 586:
... West Farms, Kingsbridge, Mott Haven, North New York, Port Morris, Melrose, Woodstock, Highbritlgeville, Claremont, ...
 
27 June 1888, New York (NY) Times, “Room for Many Millions,” pg. 9, col. 5:
About Mott Haven and North New-York the population is largely American, with about the same average foreign representation as is contained in the district just south of the Harlem River.
 
Google Books
The City of New York:
A Complete Guide
New York, NY: Taintor Brothers & Co.
1890
Pg. 11:
North of Harlem Biver are Mott Haven, Morrisania, West Farms, North New York, Port Morris, Woodstock, Highbridgeville, Claremont, Tremont, Mount Hope, Mount Eden, Fairmount, Belmont, Fordham, and Williamsbridge.
 
Google Books
The Bronx
By Evelyn Gonzalez
New York, NY: Columbia University Press
2006
Pg. 22:
North New York, the last section to make up Mott Haven, was developed in 1860, when Robert Campbell and Edward Willis purchased 80 acres bounded by Boston Road, Brook Avenue and 138th Street for more than $204,000.
       
Twitter
Jay Pegram
‏@CaveJohnson_NYC
http://twitpic.com/1cwwwa
I am discovering St. Ann’s / St. Mary’s Park in the Woodstock / North New York Neighborhoods of the Bronx
10:47 AM - 3 Apr 2010
 
Twitter
The Gorgeous Gangsta
‏@BossNate_Stacks
Apparently there’s a north new york in the south bronx, east new york in brooklyn, and west new york in jersey… Can’t find a south ny tho
10:01 AM - 14 Jan 2011
 
Twitter 
Desus Nice
‏@desusnice
Thats right fam, the bronx is officially “NORTH NEW YORK”.
2:24 PM - 12 Mar 2013
 
Twitter
Eric Hoke
‏@erichoke
Dear NYC Real Estate Agents. It’s The Bronx. Not “North New York”
7:57 AM - 18 Apr 2015
 
Twitter
Alex Silverman
‏@AlexSilverman
Wait, so real estate people are now calling this part of the #Bronx “North New York” ??
5:43 PM - 20 May 2015
 
Twitter
Chase N. Greene
‏@iAmJThomas1
@JLo what u think about Ny changing the name of ur hood..South Bronx to “North New York”
9:44 AM - 17 Jun 2016
Manhattan, NY
   
Curbed—NY
New York City Rent Comparison: What $2,000 Gets You Right Now
See what $2,000 rents in NYC neighborhoods like Bushwick and Midtown East
BY AMY PLITT @PLITTER JUL 5, 2016, 2:48P
(...)
In the Bronx—North New York, specifically—a three-bedroom, one-and-a-half bathroom apartment is asking $1,999.
(...)
COMMENTS
REspectator
North New York: Is that the new name for the South Bronx?
Posted on July 5, 2016 | 8:05 PM
   
DNAinfo—New York
How Mott Haven Real Estate Listings Show Blurring Neighborhood Boundaries
By Amy Zimmer | July 7, 2016 2:40pm
(...)
“This newly renovated building is in the highly desirable Mott Haven neighborhood of the south Bronx,” the listing from Atelier Properties states.
 
Another indication of the fluctuation of neighborhood names, the real estate search engine Streeteasy,  denotes the eastern part of the neighborhood as a separate area called “North New York,” which was its historic name.
   
Twitter
Sweet Violet
‏@SweetVioletNY
@streeteasy calling South Bronx “North New York” now. Harlem is north NY. #gentrification be honest. It’s ok.
12:14 PM - 30 Aug 2016