The house, along with the neighboring structure at 7 East 72nd Street, has been owned since 2002 by the government of Qatar, which has combined the two buildings into a single residence.

The house originally spanned 25,363 square feet (2,356.3 m2), with various living spaces on the second floor and bedrooms on the upper stories.

The Lycée Français de New York, which already occupied the neighboring mansion at 7 East 72nd Street, moved into the house in 1964.

The school vacated 7 and 9 East 72nd Street in 2002, when they were sold to Hamad bin Khalifa Al Thani, the Emir of Qatar.

After the Qatari government finished renovating and combining the buildings in 2010, the two structures comprised New York City's largest single-family residence.

The westernmost bay includes a round-arched entryway, which in turn is topped by a cartouche flanked by scrolled brackets.

[13] This hall measures 22 by 28 feet (6.7 by 8.5 m) and contains leaded glass windows, oak-and-iron doors from the entrance, a large fireplace, and a plaster ceiling with classical design details.

[6] The Sloanes lived on 54th Street until the 1890s at a time when that part of Midtown Manhattan was filled with houses for the upper class.

[8] Initially, Sloane wanted to hire both McKim, Mead & White and Richard Morris Hunt to design competing plans for the house.

[29] Jessie, who frequently communicated with friends via a messenger call box in the house, found that some of her messages were intercepted after the couple had separated.

Under the terms of the divorce, Jessie gave up the 72nd Street residence and agreed not to visit her two daughters until they turned 21 years old.

[39] By 1905, Stillman was recorded as having shifted his primary residence out of New York City, though he continued to live at 9 East 72nd Street.

[10] Although he hosted events such as a reception for his son's wedding in 1911,[42] The Buffalo News described the house the next year as one of several empty mansions in New York City.

[44] The carpet manufacturer and former U.S. representative John Sanford leased the house for a short time[45] before buying it in April 1919 at an estimated value of $500,000.

[vi][45][46] The Sanfords hosted events such as lecture-musicals,[47] a dinner honoring their son Stephen,[48] and debutante balls for their daughters Sarah and Gertrude.

[51] Stephen Sanford was recorded as living at the house until he married the actress Mary Duncan in 1933,[52] as did Sarah until her own marriage in 1937.

[56][58] The New York Herald Tribune reported in December 1946 that Mathews and Dudgeon transferred ownership of the house in December 1946 at an estimated value of $200,000,[vii][59] but the Herald Tribune and The New York Times both record Harold Churchill Mathews as having owned the house through the next year.

[viii][60] After Boos's acquisition, the house was occupied by the Sanctuary of the Master's Presence;[55] the interiors remained mostly unchanged even after its conversion to religious use.

In April 1964, the Lycée Français de New York, a French-language school, purchased 7 and 9 East 72nd Street from the Boos family for a combined $850,000.

[62] Lycée Français formally opened its classrooms at 9 East 72nd Street on September 24, 1964; the school hosted classes in one of the houses' old ballrooms due to a lack of space.

[7] After Lycée Français developed a new building on York Avenue in the 2000s, the school originally considered keeping the six townhouses that it owned, including the houses at 7 and 9 East 72nd Street.

[70][71] Dozens of buyers expressed interest in the house, of which real estate broker Barbara Corcoran estimated that half wanted to convert it into a single-family home.

[71] The 72nd Street houses remained unsold for over two years because of a decline in New York City real estate following the September 11 attacks.

[7][72] The purchaser of the buildings was Hamad bin Khalifa Al Thani, then the Emir of Qatar,[4][73] who reportedly beat out the developer Donald Trump and an unknown bidder when he agreed to acquire the properties in August 2002.

[37] The combined mansion at 7–9 East 72nd Street covered 45,000 square feet (4,200 m2), making it New York City's largest single-family house.

[72] Qatari Sheikha Al-Mayassa bint Hamad Al Thani used the houses as her New York City residence, displaying her art collection across numerous rooms.

[6] In 1900, Architectural Annual magazine described 7 and 9 East 72nd Street as "Enigmas: Hotels particuliers a New York – but not the French Quarter" in a picture caption.

[15] A writer for The New York Times described the house in 1974 as "perhaps the finest of the Gallic limestones" to be developed around the Upper East Side's millionaire's row.

[11] Christopher Gray of The New York Times wrote in 2011 that the house's design was "ultra-French" but was beaten out by the neighboring 7 East 72nd Street.