Brooklyn is well-known for its brownstone houses, built mostly between 1840 and 1900. The unofficial “brownstone belt” neighborhoods include Brooklyn Heights, Stuyvesant Heights, Fort Greene, Park Slope, Carroll Gardens, Cobble Hill, Boerum Hill, Clinton Hill and Vinegar Hill. Brownstone houses were seldom constructed after 1900, when the New York City subway and the automobile encouraged home-building further away from Manhattan.
 
The term “brownstone belt” is cited from the 1970s and has been used mostly since the 2000s, when the brownstones attracted the attention of historic preservationists. Fifth Avenue in Manhattan was called a “brownstone belt” in 1926 by a syndicated newspaper columnist, but the Manhattan usage has been rare.
     
     
Everything2.com
Brownstone Belt
by Purvis
Wed May 16 2001 at 21:06:41
Term for the large swath of Brooklyn neighborhoods dominated by elegant Brownstone architecture, the largest concentration of such architecture in the world.
 
Brownstones were the popular form of upper middle class housing built in America from the 1840s through around 1900. They usually featured rows of elegant, mostly identical stone row houses, sometimes featuring imposing porches, fancy staircases, and elaborate Victorian interiors. Brownstone developments were usually built all at once or block by block by major developers on previously undeveloped land, much like today’s suburban subdivisions, although in a more beautiful and much less environmentally destructive and tacky way.
 
Throughout much of the era in question, the city of Brooklyn was a suburban town for the upper middle class, and consequently Brownstone architecture dominates the neighborhoods that were developed in that era. The first Brooklyn neighborhood to be populated was Brooklyn Heights, directly across from Manhattan, which became fashionable in the 1840s after regular ferry service made it possible to commute to Manhattan for work. The brownstones in Brooklyn Heights are some of the oldest and most elaborate in America.
 
In the following decades, brownstone development proceeded from Brooklyn Heights south to the adjacent neighborhoods of Cobble Hill, Clinton Hill, and Vinegar Hill, and farther south to Caroll Gardens, which was a large planned community with elegant gardens. At this point the primary method of transportation for these suburbanites was still the horse and carriage, so many of the homes and neighborhoods were built to accommodate them. With the emergence of the network of elevated commuter railways in Brooklyn in the last half of the 19th century, and the opening of the Brooklyn Bridge, and elevated transit links to Manhattan (see Brooklyn Manhattan Transit), many new areas were opened to development, and this 19th century version of suburban living became accessible to many more people. The brownstone districts of Fort Greene and Prospect Heights were built to the east of downtown Brooklyn along the Lafayette Avenue and Fulton Avenue elevated lines respectively. Prospect Park and Fort Greene Park were developed as playgrounds for these neighborhoods.
 
In the 1880s and 1890s, brownstone developments advanced further, as the city of Brooklyn consolidated all of Kings County. Park Slope emerged on the Western side of the new Prospect Park, served by the Fifth Avenue Elevated, and to the east of Prospect Heights along the Fulton elevated Bedford-Stuyvesant emerged. As the brownstone era drew to a close, the northern area of Windsor Terrace, to the south of Park Slope, was developed, as were a few blocks on the eastern side of Prospect Park, part of Prospect Lefferts Gardens.
   
(Oxford English Dictionary)
brown-stone, (a) (see quot. 1875); (b) U.S., one or other variety of a dark-brown sandstone used for building; also ellipt., a house built of brown-stone, and attrib. and transf., designating the well-to-do
[1836 Knickerbocker VIII. 390 His poor remains..in one corner.. a brown stone at his head and foot.]
1858 Spirit of Times 13 Feb. 377/2 A solid substantial *brown-stone front house.
1865 ‘G. HAMILTON’ New Atmosphere 32 The brown-stone friends are shocked and scandalized.
1875 tr. Vogel’s Chem. Light xvii. 270 Hyper-oxide of manganese also named brownstone. 1909 ‘O. HENRY’ Options 22 Two old-fashioned, brownstone front residences.
1948 Time 8 Mar. 25/1 Nightclubs in sorry brownstones.
1957 New Yorker 21 Sept. 132/3 The part of Brooklyn we were riding through was..lined with old and ugly brownstones.
 
30 July 1926, Athens (OH) Messenger, “In New York” by Gilbert Swan, pg. 4, col. 3:
Old Brownstone “Fronts” Are Disappearing Rapidly.
NEW YORK, July 30—Long since, the passing of the “brownstone age” has been heralded by the merciless banging of the trip hammers on the steel skeletons of modern apartment dwellings.
 
Today the total number of private mansions along the Avenue is about 200, and in that good old “brownstone belt” from 44th to 100th Street the number is now less than a hundred.
(Fifth Avenue in Manhattan—ed.)
 
Google Books
15 November 1976, New York magazine, ‘The Passionate Shopper” by Barbara Sharnik, pg. 134, col. 2:
Here in my part of Brooklyn — the brownstone belt just across the East River from Manhattan— canny bargain- hunters spend their late-November weekends scouting the local church bazaars.
 
4 November 1986, Newsday, “Local Papers Slug It Out: Park Slope’s affluent new residents are the prize as community newspapers battle for advertisers and display space” by Susan Brenna, pt. 2, pg. 3:
She also believes the phenomenon will be repeated in other parts of the brownstone belt.
 
Google Books
Guide to New York City landmarks
By Andrew Dolkart; Marjorie Pearson; New York (N.Y.). Landmarks Preservation Commission.
Washington, DC: Preservation Press, National Trust for Historic Preservation
1992
Pg. 7:
In Brooklyn, neighborhoods in the brownstone belt — Brooklyn Heights and Stuyvesant Heights, Clinton Hill and Cobble Hill, Park Slope and Fort Greene — are complemented by turn-of-the-century planned suburbs such as Prospect Park South and the old commercial precincts around the Fulton Ferry landing.
     
New York (NY) Daily News
AISLES OF JOY COMING TO LIFE
BY DENIS HAMILL
Friday, July 26th 1996, 2:00AM
(...)
Now, in a once culturally moribund neighborhood, young people flock on dates, the elderly arrive in safe groups for the special senior citizen prices, the yuppies of the brownstone belt of Park Slope come for the art films in the small screening room.
 
New York (NY) Daily News
HOW CRIME KEEPS MY COZY NABE SAFE
BY DENIS HAMILL
Sunday, January 25th 1998, 2:03AM
(...)
All of this came to mind last week as I also remembered a few months ago stopping to look in a real estate window down on Seventh Ave. in the fashionable brownstone belt of Park Slope.
 
New York (NY) Times
State Seeks Plans for Neglected Brooklyn Area
By JOSEPH P. FRIED
Published: November 15, 2000
(...)
Boerum Hill is one of the districts forming a so-called brownstone belt around much of downtown Brooklyn’s bustling commercial core.
 
New York (NY) Times
May 11, 2008
Brooklyn Churches Come and Go
By C. J. HUGHES
(...)
Such transformations have notably made a mark in Brooklyn’s “brownstone belt,” the cluster of 19th-century buildings ringing downtown from Carroll Gardens to Clinton Hill.