Manhattan’s Gracie Mansion, built in 1799, has been the mayor’s official residence since Mayor Fiorello H. LaGuardia moved there in 1942. Mayor Michael Bloomberg declined to live there, but helped to renovate it and often held public functions there. The Bloomberg administration referred to Gracie Mansion as the “People’s House” by at least 2002.
 
Gracie Mansion has often been called the “Little White House,” after the U.S. president’s White House. “Little White House” has been cited in print since at least 1943.
 
   
NYC.gov—Gracie Mansion: The People’s House
A Brief History of Gracie Mansion
In 1799, a prosperous New York merchant named Archibald Gracie built a country house overlooking a bend in the East River, five miles north of the City. Financial hardship forced Gracie to sell his house to Joseph Foulke in 1823, and, in 1857, Noah Wheaton purchased the property. In 1896, the City of New York appropriated the estate due to non-payment of taxes, incorporating its 11 acres of grounds into East River Park, renamed in 1910 for the German-American statesman, Carl Schurz.
 
After decades of use as a concession stand and as restrooms for the park, Gracie Mansion was restored and became the first home of the Museum of the City of New York. When the museum moved to its larger permanent building on Fifth Avenue on January 11, 1932, Gracie Mansion became a historic house museum run by the Parks Department. Parks Commissioner Robert Moses finally convinced city authorities to designate the house as the official residence of the Mayor and, in 1942, Fiorello H. La Guardia moved in as the First Mayor of New York City to reside at Gracie.
 
Its tradition as New York’s “Little White House” thus began, allowing it to serve as a place where history is made, not merely recorded.
   
Wikipedia: Gracie Mansion
Archibald Gracie Mansion (commonly called Gracie Mansion) is the official residence of the Mayor of the City of New York.[2] Built in 1799, it is located in Carl Schurz Park, at East End Avenue and 88th Street in the Yorkville neighborhood of Manhattan. The mansion overlooks Hell Gate channel in the East River.
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In 1942, Robert Moses convinced Mayor Fiorello H. La Guardia to appropriate the house as a mayoral residence. Its main two floors are open to the public on a limited basis for guided tours and serve as a small museum.
 
It was added to the National Register of Historic Places in 1975.
 
Old Fulton NY Post Cards
29 March 1943, Brooklyn (NY) Eagle, “Heffernan Says: Gracie Mansion And City Taxes,” pg. 6, col. 5:
It is unfortunate that minor details have been allowed to becloud the question of municipal taxation. The instance I have in mind is the occupation of Mayor LaGuardia for residential purposes of the Gracie Mansion, as his own little White House. Park Commissioner Moses says the maintenance of this domicile, which formerly was the Museum of the City of New York, is merely incidental to the upkeep of Carl Schurz Park and the cost inconsiderable. He is quite right.
 
16 March 1947, Atlanta (GA) Constitution, “Comfort for Willie O’s Widow” by Warren Hall, magazine, pg. 18, col. 1:
THE embers of a party were still glowing at Gracie Mansion, New York City’s “Little White House” and the resident of Mayor William O’Dwyer.
   
Google Books
The American Mercury
Volume 81
1955
Pg. 20:
Within a few days, long- neglected Gracie Mansion was back on page one. ... even before the Mayor had a housewarming, economy-minded groups were protesting the erection of an iron fence around the Little White House over Hell Gate.
Pg. 21:
WHEN WILLIAM O’DWYER followed LaGuardia to the Little White House, his wife, former fashion model Sloan Simpson had the place redecorated, thereupon bringing more squeals from taxpayer groups.
     
Curbed—New York
How Gracie Mansion Became New York’s ‘Little White House’
Friday, January 3, 2014, by Curbed Staff (James Nevius)
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Bloomberg’s administration has taken pains to re-brand the mansion as the “People’s House,” implying greater public access and a criticism of any future mayor who chooses to live there. But Bloomberg does have a point: in the home’s long history, its role as the mayoral residence is relatively new. In fact, de Blasio will be only the tenth mayor to live there; the first was Fiorello La Guardia, who took up residence in May 1942. And he had to be practically dragged into the place.
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Should the de Blasios live there? The new mayor’s “two cities” rhetoric notwithstanding, Gracie Mansion has come to be—in the words of H.L. Mencken’s American Mercury magazine—New York’s “Little White House.”
 
Untapped Cities—New York
10 Secrets of Gracie Mansion, NYC’s Little White House
02/11/2016 at 9:00 am
by vera penavic
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In 1942, famous Parks Commissioner Robert Moses vehemently pushed city authorities to make this historic house the official residence of the Mayor Fiorello H. La Guardia, but he had no interest in living there. Moses convinced La Guardia to move for “national security” reasons. (...) Convinced, La Guardia moved in as the First Mayor of New York City resident of Gracie Mansion. He was so enamored with the house that he nicknamed it the “Little White House.”