Mary Harris was born in the destitute slums of Cork, Ireland on August 1, 1837. Like many of their countrymen, the Harris family had moved to Cork to escape the desperation and dying economy of their native village, Inchigeelagh. According to documents, the Harris family held on to a small plot of land in Inchigeelagh, but their property there most likely only provided them with a few meager crops, such as potatoes. Like most Irish parishes in the nineteenth century, Inchigeelagh was populated by Irish Catholics, but most of the land was owned by English Protestants, whose privileges allowed them to charge high rents, leading to the impoverishment of the local population.
Mary Harris and her family spent nearly a decade living in both Cork and Inchigeelagh. Harris most likely grew up in the most densely populated part of the city, an overcrowded area of slums that absorbed the migrants from poverty- stricken rural parishes. While growing up, Harris witnessed the harsh economic realities resulting from the growing market economy and the continuous loss of Irish sovereignty to English dominance. Riots and revolts threatened to hinder English policies, but resistance was punished harshly. During the winter of 1821 to 1822, hundreds of desperate men, under the leaderships of an enigmatic Captain Rock, raided the homes of wealthy families. The army pursued them, and the Rockites fought back and eventually dispersed. As a result of this conflict, many Irishmen were brought to trial, hanged, or deported to Australia. Famine and poverty increased as a fungus damaged the potato crop, which was the main source of sustenance for the majority of the Irish population. The Irish Potato Famine was immensely destructive. Mass evictions exacerbated the situation, and English efforts to relieve the starvation were negligible. In 1847, when Mary Harris was ten years old, her father and her brother left for America, along with approximately 200,000 emigrants that year alone. Harris's mother managed to keep the rest of the family alive until they departed for America in the early 1850s.
Mary's father, Richard Harris, awaited the family in Toronto, Canada, where he and his son probably worked as laborers for the Canadian railroads. The children attended Canadian school and continued to be raised in the Irish Catholic tradition. In fact, one of Mary Harris's brothers even studied to become a priest. The family's economic situation improved, and they were able to rent their own small home. However, Harris's family still had to work hard to provide for themselves, gardening their small plot of land, and keeping cows and chickens.
Mary Harris continued her education beyond primary school by studying to become a teacher. She also learned how to make dresses, a skill that later became useful. After gaining a certificate from a priest attesting to her good moral character, Harris was accepted into the Toronto Normal School in 1857. This accomplishment was rare for immigrants, especially for Irish Catholics. She studied at this prestigious school until the spring of 1858, receiving enough education to be ready for a teaching job at a convent in Monroe, Michigan in 1859.
Although Harris herself attested to being born in 1830, there is no documentation confirming this date, and it is possible that she exaggerated her age to better fit her maternal image in the labor movement. Little is known about Harris's early childhood, but as she herself attested, her relatives were most likely part of the poor Irish laboring masses. In her autobiography, Harris did not devote many pages to describing her early childhood, but she most likely witnessed the destitution of the countryside and the urban slums. Many Irish families developed a mythology that linked them to Irish freedom fighters, but there is no documentation that attests to the fact that Mary Harris's relatives were engaged in rebellion against the English. However, Harris probably grew up with a strong sense of her ethnic and religious heritage, and with a personal courage strengthened by the tremendous tragedy and hardships that she had already overcome.