McKinney was born Louise Crummy on 22 September 1868 in Frankville, Ontario, the sixth of ten children of Richard Crummy and Esther Empey. Her father had immigrated from Ireland to settle in Upper Canada in 1842, later bringing his wife in 1857. McKinney graduated from Athens High School intending to become a physician but faced difficulty entering medical school due to her gender. Instead, she attended Ottawa Normal School to become a teacher. She taught for four years in Ontario before moving to North Dakota, where she taught for three more years.
