The Palazzo Rezzonico is now known as the Ca' Rezzonico. 

In 1880 it was owned by Robert Browning's son who had purchased it with his wife's money and was in the process of restoring it. Because of his father's artist affiliations the place became somewhat of a magnet for other artists. In '80 Sargent set up a studio there where he meets other artists who had studios inside -- Giovanni Boldini being one and possibly runs into James Abbott McNeill Whistler during this trip. 

Robert Browning lived here with his son briefly in 1888–89 when he was in failing health and where he eventually died. In 1881 the elder Browning was also painted by four different artists at Rezzonico including Sargent's friends Ralph Curtis, and Charles Stuart Forbes. 
 

In 1935 the Venice City Council bought the palazzo and created the Museum of Eighteenth-Century Venice which it is today.

The building was first started in 1649. The Bon family of Venice commissioned the architect Baldassarre Longhena to build the the palace making it a baroque, but because of financial difficulties the Bons sold the property to Giambattista Rezzonico, a Lombardy merchant and banker. He hired the architect Giorgio Massari to finish it.

In 1748 Carlo, Giambattista Rezzonico's son, became Pope Clement XIII, no bad for a son of a banker. The interior decorating was begun in 1752, and the greatest artists then  working in Venice were called in, who include Giambattista Tiepolo, Gaspare Diziani and Jacopo Guarana. Tiepolo painted the ceiling frescoes for the room now known as the Nuptial Allegory Room and for the Throne Room (Allegory of Merit), which were the artist's last works before leaving Venice. Gaspare Diziani painted the fresco in the Pastel  Room, showing the Triumph of Poetry, while Jacopo Guarana painted the Allegory of the Virtues fresco in the Tapestry Room.

Notes:

• Overview of Venice