Mary Arthur McElroy

Mary McElroy (née Arthur; July 5, 1841 – January 8, 1917) was an American woman known as being the sister of the 21st president of the United States, Chester A. Arthur, for whom she served as a hostess (acting as the first lady) for his administration (1881–1885). She assumed the role because Arthur's wife, Ellen, had died nearly two years earlier.

McElroy was born in New York and attended the progressive Emma Willard School. She married insurance salesman John Edward McElroy and worked for some time as a teacher. When her brother Chester A. Arthur became president, she lived in the White House during winter months to host social events and care for her niece. As acting first lady, McElroy ended the tradition of suspending social events during Lent, and she held large weekly receptions. She was a popular hostess, and contemporary Washington social life celebrated her for her lively receptions.