19 Gramercy Park South, Historic mansion at Gramercy Park South, New York City, United States.

19 Gramercy Park South is a four-story row house at the corner of Gramercy Park South and Irving Place, known also as 86 Irving Place or the Stuyvesant Fish House. Its 37 rooms cover 18,000 square feet and include a marble staircase, a library, two kitchens, a wine cellar and a top-floor ballroom.

William Samuel Johnson built the house in 1845 as 86 Irving Place; Horace Brooks later added a fifth story and a stable. In 1887 Stanford White remodelled it for $130,000 into a mansion with a marble staircase and a top-floor ballroom, and the address became 19 Gramercy Park. The Fish family left in 1898 and the house was divided into apartments.

The address 19 Gramercy Park did not exist before 1887; Stanford White's remodeling created it. Mamie Fish's parties in the top-floor ballroom brought old-money New York together with show-business figures, and Benjamin Sonnenberg continued that mix after 1931. Jack Finney's 1970 novel Time and Again places a boarding house at this address.

The building sits at the corner of Irving Place with convenient access to nearby subway stations and many restaurants around the neighborhood. The adjacent Gramercy Park is private and limited to residents, but the surrounding streets are pleasant to explore on foot.

Benjamin Sonnenberg bought the entire building in 1945 and filled its rooms with English furniture and drawings by Old Masters. This transformation into a private art collection made it a distinctive gathering place for collectors and art lovers.