Mary Rebecca died on 24 February 1886 in New York (Manhattan), and was buried in Green-Wood Cemetery two days later. It is possible that her remains were later moved to Saint James Episcopal Churchyard in Hyde Park, New York, as that is the location of her tombstone. See further discussion regarding her burial site on her FindaGrave profile.
↑ "New York, New York City Municipal Deaths, 1795-1949," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:2WJ5-RLR : 20 March 2015), Mary R. Roosevelt, 24 Feb 1886; citing Death, Manhattan, New York, New York, United States, New York Municipal Archives, New York; FHL microfilm 1,373,982.
United States Census, 1850," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MCYW-HP5 : 12 April 2016), Mary R Roosevelt in household of Isaac Roosevelt, Hyde Park, Dutchess, New York, United States; citing family 222, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).