Margaret Olivia Slocum Sage (8 September 1828-4 November 1918) was an American philanthropist. Upon the death of her husband Russell Sage she received a fortune estimated at more than $50,000,000, to be used as she saw fit. She was born in Syracuse, New York and graduated from the Troy Female Seminary (later called the Emma Willard School) in 1847.
In 1905, Olivia Sage informed Syracuse University of her willingness to purchase Yates Castle and its surrounding property to house a teachers' college for the university. Olivia had begun to act independently of Russell Sage in a project that combined her attachment to Syracuse, her self-identification as a teacher, and her commitment to women's education. Her greatest single benefaction was the gift of $10,000,000 in 1907 to establish the Russell Sage Foundation. In 1908 she donated $650,000 to Yale University, enabling the purchase of the Hillhouse property for Yale's expansion. In 1909, she donated Holder Hall to Princeton University, named after her ancestor Christopher Holder. Two years later, Sage gave $300,000 to Cornell University for the construction of a women's dormitory, Risley Hall, named after her mother-in-law. Her promotion of women's education also included funding the construction of the Olivia Josselyn House, named after her mother, at the then all female Vassar College in 1912. Also in 1912, she acquired Marsh Island in the Gulf of Mexico and dedicated it as a home for wild birds. In 1916, she founded Russell Sage College in Troy, New York. Later, in 1919 she gave $2,750,000 for the development of the Russell Sage Foundation Homes, a suburban community at Forest Hills Gardens, Queens. In addition she gave extensively to the Rensselaer Polytechnic Institute (RPI) and the Emma Willard School. Up to 1915, the sum total of Sage's gifts surpassed $23,000,000.
Olivia Sage also organized the effort to fund and build the John Jermain Memorial Library in Sag Harbor in honor of her grandfather, Major John Jermain, who fought in the American Revolution. The library was designed by Augustus N. Allen and presented as a gift to the people of Sag Harbor in 1910. The property was bought at a cost of $10,000, and was directly across from Sage's then summer home on Main Street. At that time, it was the highest price ever paid for a piece of real estate in Sag Harbor.
Mrs. Sage also used a large portion of her money to create Russell Sage College. Russell Sage College is a comprehensive college for women nestled within the historic district of Troy, NY. RSC offers liberal arts and professional degree programs in an environment aimed at empowering students to become women of influence in their careers and their communities.
She lived for many years in the building that is now the Sag Harbor Whaling Museum.