In 1870 the Seven Sisters of St. Joseph of Carondelet, Missouri traveled to Tucson to open a school. Bishop Jean Baptiste Salpointe pleaded with them to open a much needed hospital since the railroad was about to arrive and along with it a larger population.
On April 24, 1880, one month before the railroad arrived, the hospital opened with 12 beds. Dr. John C. Handy was its first physician. In the next 10 years it added a 24-bed isolation cottage for TB patients.
Today St. Mary's is recognized as Arizona's oldest hospital with the busiest emergency room in the city.