The Ross–Hand Mansion is an historic home located at South Nyack in Rockland County, New York. The land was acquired from Garrett J Tallman (1784-1862) for $5,000 in 1856 by Azariah Ross (1787-1878). The Tallman family had occupied the land since 1675-76 when Harmen Douwenszen Taelman (1655–1691) came to camp on his father’s land after an Indian deed had been signed and royal patent issued. Azariah Ross was a veteran of the War of 1812 and a successful New York City property developer. He was a longtime resident of Rockland County, having moved there in about 1820. The design of the Mansion is closely based on a design for 'A Country House in the Pointed Style' from the Architecture of Country Houses: including designs for cottages, farm-houses, and villas, with remarks on interiors, furniture, and the best modes of warming and ventilating by the great landscape designer and architect Andrew Jackson Downing. The three-story brick mansion with Gothic Revival style features was completed by April 1859. It features ornamental bargeboards and a steeply pitched gable roof.

Azariah Ross was instrumental in extending the Northern Railroad to Nyack. On May 28, 1870, he hosted in the grounds of the Ross–Hand Mansion a celebration of the arrival of the rail line. A banner was strung over the entrance reading 'Welcome to Nyack, the Gem of the Hudson' surrounded by fluttering flags. The chairman of the reception committee, Seth B Cole, gave a fulsome welcome to the crowds on the Mansion's lawn: “Nyack embosomed in the semi-circling hills that adorn the west bank of the noble Hudson at Tappan Zee - in possession of beauty and wealth of attractions rarely equaled, has cherished the unfolding hope ... when appreciative, intelligent, worthy and wealthy votaries shall seek and find a resting place in her bowers. Nyack in slumbering loveliness, has dreamed of this joyful hour”.

By 1871, trying to stave off financial uncertainty, Ross converted his house into a hotel, the Ross Mansion. Note that in the application packet to have the house considered for inclusion on the National Register of Historic Places, one source incorrectly attributes another name to the house during its years as a hotel. On May 8, 1883, after Ross' death, the home was purchased at a public auction hosted by A J Bleeker in New York City by Mary Elizabeth Haddock Hand (1836-1917). Mary's husband, William Henry Hand (1837-1898), specialized in decorative woodwork and, with their sons William, Roger and Walter, he completed extensive renovations on the property and installed elements, including a marble fireplace, from the Alexander Turney Stewart Mansion on Fifth Avenue in Manhattan that had recently been demolished. They converted the rear part of the property into a working farm with help from a lodger named Robert Latimer who had previously managed a family farm in West Nyack.

Hand's grandson, also named William Henry Hand (1900-1978), was an assistant to an elderly Thomas Edison. However, strong ethical differences over Edison's business practices led Hand to set out on his own and by 1930 he had established the Hand Laboratory for Electro-Chemical Research and Development in a barn on the grounds of his family's South Nyack mansion. There, over the next thirty years, Hand and his small team developed a long-life battery that was used by emergency services, the military, public works vehicles, school buses and in boats.

William Henry Hand lived at the house with his brother Raymond (1899-1972), sister Dorothy Crawford (1903-1995) and her daughter Adelma. When William died in 1978, Dorothy and Adelma and Adelma's children were the remaining occupants. In the early 1990s when Adelma wanted to list the property for sale, the analysis of soil samples found dangerous levels of lead contamination: over three decades of battery development, it appears that battery acid, lead and other experimental material was dumped on the grounds of the mansion. The property was deemed a risk to human health and placed as a Class 2 site on the New York State Department of Environmental Conservation Division of Hazardous Waste Remediation register of Inactive Hazardous Waste Sites, #344040. Adelma undertook a private remediation on her property. The NYS DEC performed additional soil testing of neighbouring properties and implemented their full remediation with state funds. The area was finally considered safe and removed from the NYS DEC register in 1998.

Also on the property is a 19th-century barn and stable with a gymnasium (in the former battery laboratory) and a small brick smokehouse. The Mansion's original summer kitchen was located to the rear of the property and was demolished in about 1999.

In June 1997, the Mansion was the venue for the Hudson River Designer Show House with rooms reimagined by a number of designers including Louis Navarrete, Jean-Pierre Dovat and Mario Buatta.

The property was sold in 1998, then again in 2014 and, most recently, in 2019.

The Ross-Hand Mansion was listed on the National Register of Historic Places in 1983.