English: First operating room, St. Joseph's Hospital Chatham, Ontario.

In 1890, a meeting was held between Reverend Paul, O.F.M. of St. Joseph's Parish, Reverend Mother Ignatia Campbell, and Mother Aloysia Nigh, along with some of the prominent doctors of Chatham. They decided that the community was in need of a hospital and the sisters agreed to run it. A boarding house, formerly the Salvation Army Barracks, was leased until funds could be secured for a new hospital to be built. The hospital was officially opened in its temporary quarters on October 15, 1890, with Mother Aloysia as its head, assisted by Sisters Francis and Martha. Construction began at the hospital's long-time site of 519 King Street West on the Thames River with the laying of the cornerstone in 1891. Construction was completed in 1892. Over the years, wings were added onto the hospital to accommodate the growing community of Chatham and, therefore, the growing demand for hospital services. These additions were built in 1901, 1912, 1936 and 1956.
By 1945, the hospital had 117 beds.

In 1972, the amalgamation of services occurred between St. Joseph's Hospital and Public General Hospital as ordered by the Ministry of Health for financial reasons. Legislative changes, increasing government control, and the decline in numbers of Sisters working in the health care field led to the gradual withdrawal of the Sisters from the hospital. The last year that a Sister was a hospital administrator was in 1984. In 1992, the Sisters withdrew from residence at the hospital, and in 1993, the ownership of the hospital was taken over by the St. Joseph's Health Care Society. At the time it was an acute care facility with chronic beds as well. In 1993, the hospital had 173 beds.