McCool was born on 13 December 1909. She lived on St. Joseph Island, Ontario until she was 20 years old, when she moved to Sault Ste. Marie, Ontario.
In 1938, she married George Cahoon. They had one daughter, Patricia Allan (1940–2012). In 1950, she divorced. In the 1960’s, she remarried to Loren McCool. She worked in a variety of grocery stores as well as a proofreader for the Sault Star, also working as a candy striper at the Sault hospital.
At the age of 101, she came to reside at the assisted living building (Kotitalo) at the Ontario Finnish Resthome. At the age of 107, in June 2016, McCool transitioned into 24-hour nursing home care at Mauno Kaihla Koti.
McCool died in Sault Ste. Marie, Ontario, Canada on 11 March 2021 at the age of 111 years, 88 days.
Her age was verified by Stefan Maglov, and validated by LongeviQuest on 17 February 2023.