Mary Scott McKee (nee Harrison; April 3, 1858 – October 28, 1930) was the acting First Lady of the United States for her father Benjamin Harrison. She lived in the White House for the duration of her father's presidency where she worked as an assistant to her mother, first lady Caroline Harrison. She became the acting first lady after her mother's death in October 1892 and remained in the role for the final months of her father's presidency. McKee's young son, known as Baby Harrison, was a popular national figure during the Harrison administration. She disassociated from her father following his marriage to her young maternal cousin Mary Dimmick.

Mary Harrison was born in Indianapolis^[1] on April 3, 1858, to Benjamin Harrison and Caroline Harrison.^[2]: 10 She attended private school as a child,^[3]: 10 and she was taught piano and painting by her mother.^[3]: 8 She wished to learn dance as a teenager, but her father forbade it on religious grounds.^[3]: 64 After completing high school, she was then sent to Philadelphia where she attended the Chestnut Street Female Seminary.^[2]: 21 When her father was elected to the United States Senate, she joined him in Washington, D.C., though she found herself unhappy with the city.^[3]: 205

Harrison was bridesmaid at her brother's wedding, where J. Robert McKee was usher. Harrison and McKee were themselves wed on November 5, 1884. They married at the First Presbyterian Church and held their reception at the Harrison family home. They moved into this home after their honeymoon, while Mary's parents lived in Washington.^[2]: 25

Mary McKee gave birth to her son, Benjamin Harrison McKee, on March 15, 1887.^[2]: 26 When her father became a candidate in the 1888 presidential election, McKee involved herself in campaign activities, assisting her mother in managing the campaign's social aspects. Her involvement in the campaign was reduced by her responsibilities as a mother,^[4]: 53 for she gave birth to her daughter, Mary Lodge McKee, on July 4, 1888.^[2]: 27

McKee stayed with her father after leaving the White House, moving back to Indianapolis where they worked together to remodel their house.^[4]: 154 She also accompanied him in his post-presidential travels.^[10]: 277 She was upset when her father remarried in 1896, as he had chosen his wife's young niece, Mary Dimmick, as his bride.^{[9]: 336 [12]} It is unknown whether McKee disliked Dimmick prior to the announcement or when she became aware of her father's romantic interest in Dimmick.^[4]: 155 McKee did not attend the wedding,^[12] and she remained distant from her father thereafter.^{[9]: 336 [12]} Historian Charles W. Calhoun suggests that McKee was also upset because she had grown accustomed to spending her time with her father, which was interrupted by the relationship between Harrison and Dimmick.^[10]: 277

McKee avoided her father until his death in 1901.^[10]: 277 She contributed 165 items to the collection of her father's presidential papers in 1928.^[13] She received an honorary doctorate of law from her father's alma mater, Miami University, in June 1930.^[1] Mary McKee died in Greenwich, Connecticut, on October 28, 1930. She had previously moved to Greenwich with her husband.^[1] She was buried at Crown Hill Cemetery in Indianapolis, Indiana, as her parents had been. Her husband lived in Greenwich near their daughter until he committed suicide at age 84 in October 1942.^[14]