Sarah Chauncey Woolsey (January 29, 1835 - April 9, 1905) was an American children's author who wrote under the pen name Susan Coolidge. She was born into a wealthy, influential family in Cleveland, Ohio, and spent much of her childhood in New Haven Connecticut. She worked as a nurse during the American Civil War, after which she started to write. Woolsey never married, and resided at her family home in Newport, R.I., until her death. She edited The Autobiography and Correspondence of Mrs. Delaney (1879) and The Diary and Letters of Frances Burney (1880). She is best known, however, for her classic children's novel What Katy Did.