In 1950, the Sisters of Mercy opened Mercy Junior College in Tarrytown, New York for younger members of their order. In 1961, with financial assistance from the Rockefeller family, they relaunched it as a private 4-year institution for women at a new complex in Dobbs Ferry. From 1911 onward, however, the Rockefellers had a complex relationship with the Sisters of Mercy, who then lived in Tarrytown next to the main Rockefeller estate of Kykuit. While the Rockefellers' financial support of the Sisters toward the construction of a new complex in Dobbs Ferry is modest in comparison to the Rockefellers' other philanthropic endeavors in the field of education, it represents the most significant support to New York higher education outside of Rockefeller University, which Rockefeller, Sr. founded in 1901 as an institute for medical research. This article consequently explores the complex relationship between the Rockefellers and the Sisters of Mercy to illuminate a neglected aspect of Rockefeller philanthropy in their home state of New York. As a result of the Rockefellers' aid, Mercy College was able to thrive and evolve into a multi-campus, co-educational and secular institution. Today, as Mercy University, it offers nearly 100 undergraduate and graduate degree programs and its main campus in Westchester County still consists primarily of the buildings built with Rockefeller assistance.