Katherine O'Flaherty was born on February 8, 1850 (or 1851 as some critics believe) in St. Louis, Missouri to Eliza Faris O'Flaherty, a well-connected Louisiana woman with French roots, and Captain Thomas O'Flaherty, a businessman from Ireland. Her father became one of the first influences in her life. He found her natural curiosity fascinating and encouraged her interests.
On November 1, 1855, Kate's father was killed in train accident. Because of his premature death, three strong maternal figures raised Kate: her mother, grandmother, and great-grandmother. Madame Victoire Verdon Charleville, Kate's educated great-grandmother taught through the art of story telling, which is how Kate learned to be a successful storyteller. Through vivid French stories, she gave Kate a taste of the culture and freedom allowed by the French that many Americans during this time disapproved of. Many of the common themes in her grandmother's stories consisted of women struggling with morality, freedom, convention, and desire. The spirit of these stories endures in Kate's own works.
During Kate's teenage years, the Civil War raged on, separating the North and the South. Her family sided with the South, but most of her hometown of St. Louis supported the North. The loss of loved ones and the fragility of peace taught her that life was precious and needed to be treasured. Her great-grandmother Madame Victoire Verdon Charleville died in 1863 at the age of 83 and a month later, Kate's adored half-brother George O'Flaherty, a 23-year-old Confederate soldier, died of typhoid fever.
One of Kate's teachers, a Sacred Nun named Madam (Mary Philomena) O'Meara, first encouraged her to write. Writing helped Kate express her sense of humor and resolve her painful feelings of war and death. Teachers and classmates soon recognized her talent of being a gifted storyteller.