The loss of her husband and their four children, three girls and a boy (all under the age of five) in 1867, during a yellow fever epidemic in Memphis marked a turning point in her life. After that tragedy, she returned to Chicago to begin another dressmaking business. She did work for those of the upper class of Chicago in the 1870s and 1880s. Then, four years later, she lost her home, shop, and possessions in the Great Chicago Fire of 1871. This huge fire destroyed many homes and shops. Jones, like many others, helped rebuild the city. According to her autobiography, this led to her joining the Knights of Labor. She started organizing strikes. At first, the strikes and protests failed, sometimes ending with police shooting at and killing protesters. The Knights mainly attracted men but by the middle of the decade member numbers leaped to more than a million becoming the largest labor organization in the country. The Haymarket Affair of 1886 and the fear of anarchism and social change incited by union organizations resulted in the demise of the Knights of Labor when an unknown person threw a bomb into an altercation between the Chicago police and workers on strike. Once the Knights ceased to exist, Mary Jones became involved mainly with the United Mine Workers. She frequently led UMW strikers in picketing and encouraged striking workers to stay on strike when management brought in strike-breakers and militias. She believed that "working men deserved a wage that would allow women to stay home to care for their kids." Around this time, strikes were getting better organized and started to produce greater results, such as better pay for the workers.