St. Peter’s Hospital was established in 1883 by the Episcopal Diocese and incorporated in 1886.

• The earliest Hospital building was the former Grange Hall near the Pacific Railroad tracks. The Hospital then moved to a more accessible location on Jackson Street in the former residence of A. M. Holter.
  
  
• The first Hospital building was constructed in 1887 at the corner of 11th Avenue and Logan Street. A new wing was built in 1908, an addition constructed in 1932, and in 1938 a dormitory as built. The final addition to the hospital was constructed in 1957.
  
  
• In February 1931, St. Peter’s Board of Trustees amended the articles of incorporation and transferred ownership of the Hospital from the Episcopal Diocese to the Helena community for $1.
  
  
• The current Hospital building located at 2475 Broadway was constructed in 1968.
  
  
• A major construction project in 1982 added needed space to the laboratory and emergency services.
  
  
• A major construction project in 1991 added a new medical wing and made way for expanding outpatient services.
  
  
• In 1996, the Cancer Treatment Center opened, enabling Helena residents to have both chemotherapy and radiation therapy locally. The Center was expanded in 2001.
  
  
• In 1999 St. Peter’s partnered with local physicians to open the Helena Surgi-Center located adjacent to the Hospital campus.
  
  
• In September 1999, the Hospital constructed the Maria Dean Medical Office Building connected to the west side of the building.