Petit Chateau was a Châteauesque mansion at 660 Fifth Avenue on the Upper East Side in New York City. It was built for William Kissam Vanderbilt & Alva Vanderbilt from 1878 to 1882. Determined to make her mark in New York society, Alva Vanderbilt worked with the architect, Richard Morris Hunt, to create the French Renaissance-style chateau. It was sold to a real-estate developer in 1926 & demolished. In a draft of her memoirs, Alva, then Mrs. Belmont, merely noted the demolition in passing.
William Kissam Vanderbilt (1849–1920) had three houses designed by Richard Morris Hunt. His townhouse, the "Petit Château" at 660 Fifth Avenue, New York, with details drawn in part from the late-Gothic Hôtel de Cluny, Paris, proved an influential example for other Gilded Age mansions, but was demolished in 1926.