Agnes Campbell Macphail was the oldest of three girls born to Etta and Dougald on March 24, 1890 in a humble log cabin nestled in the woods of Proton Township. Although her family was poor, her parents were hardworking and determined to better the condition of life for their daughters. Even with her father working two jobs as a farmer and auctioneer, it wasn't until Etta inherited several thousand dollars that the MacPhails moved to their new home near the hamlet of Ceylon when Agnes was twelve.

She was always a headstrong child and was greatly influenced by her sharp-tongued father as well as his mother Jean MacPhail. Agnes' grandmother was forced into early adulthood at the age of twelve when her mother died, leaving her to care for her siblings. Jean learned to do men's work and never faltered in her determination; she even taught herself to read and write later in life. She was a great inspiration to Agnes as she continued to learn throughout her entire life, never growing cynical despite the hardships she faced, and most of all, her intolerance towards discrimination of any kind taught Agnes the value of humanitarianism.

School was where Aggie flourished; she viewed education as her ticket to independence and dreamed of the day when she would have her own career. Unfortunately, even after she passed the high school entrance exam, Agnes was confined to staying on the farm to help her father. It took years of convincing, but finally the young girl was admitted to Owen Sound Collegiate. Though she would have to board in Owen Sound as travelling by train every weekend was too expensive, the hiatus from school only strengthened her resolve to break through the restrictions placed on her gender.

These restrictions, however, were made more difficult for her in high school but were still not enough to keep her down. Despite being mocked for her country attire by her peers as well as dealing with a particularly harsh and sexist principal, Agnes found solace in her studies and extracurriculars. She became captain of the girl's basketball team and discovered she had an exceptional gift for making reasoned arguments during her time with the Literary Society. Agnes completed her junior matriculation in only two years, rather than the normal four, so in 1908 she went to live with her aunt and uncle in Stratford while she studied for her senior matriculation and attended the teacher's college which had opened that year.