Susan Coolidge was born in 1835 in Cleveland, Ohio, but grew up in Connecticut. During the American Civil War, Coolidge worked as a nurse. Susan Coolidge loved writing stories even when she was a child, and What Katy Did is based on Susan and her brothers and sisters when they were young. Susan, like Katy, was a high-spirited, imaginative little girl who often got into trouble.
Her realistic portrait of childhood set her apart from other writers of her time. Instead of teaching morals, she was interested in her characters, their imperfections and the dynamics of a family. The What Katy Did trilogy was a huge success.