There she saw people suffering from mental illnesses imprisoned along with criminals of all sorts. Shocked by the inhumanity of such treatment, she set out to visit every place in the state of Massachusetts where they confined the mentally ill. She found that the conditions were the same in institutions everywhere. The poor living conditions and general neglect she found throughout the state was detailed in a report to the state legislature. When improvements resulted in Massachusetts, Dix turned her attention to other eastern states and then to the West and the South.
In 1861, they then appointed Dix commissioned Superintendent of the Female Nurses of the Army, the first one in American history. Battling the stereo types, and accepting many common prejudices herself, Dix sought to ensure that her ranks are not drowned with frivolous and marriage-minded young women by only accepting applicants who were plain looking and older than 30. In addition, Dix authorized a dress code of modest black or brown skirts and forbade hoops or jewelry. Even with these strict and discretional requirements, relaxed somewhat as the war persisted, a total of more than 3,000 women served as Union army nurses. Called "Dragon Dix" by some, the Dorthea was stern and harsh, clashing frequently with the military power and occasionally ignoring administrative details. Yet, army nursing care was markedly improved under her leadership. Dix looked after the welfare of both the nurses, who labored in an often fierce environment, and the soldiers to whom they ministered, obtaining medical supplies from private sources when they were not forthcoming from the government. At the war's conclusion, Dix returned to her work on behalf of the mentally ill. .
The nearly exclusive authority of Dix to appoint nurses took a turn in 1863 when the Surgeon General issued an order that re-directed much of her power of appointment and dismissal.