The Sisters of Mercy took over the new six-story, 150-bed hospital in 1942, during the second World War.
Although it was designed to replace Queen's Hospital (site S08), both continued to operate until 1945. The Sisters of Mercy came to Maine via Bangor in 1865 and, in addition to the hospital, operated schools, day care centers, homes for aged women, and residences for working women throughout the state. Their first convent was at 100 Free Street. Their Motherhouse is now on Stevens Avenue (site SA05) next to the Catherine McAuley High School for girls (site SA04), which they opened in 1969 and named for the Irish founder of the order. The order opened St. Joseph's College in 1915 and moved it to Standish in 1955. (site S22, site M22, and site SD07.)
Eileen F. Skinner was named President and Chief Executive Officer of the hospital, the first woman to serve in those positions, in 2002. Women continue to serve in major leadership positions at Mercy.
The hospital in 2000 began its planned relocation to Fore River Parkway and completed Phase I in 2008. The entire Mercy Health System was purchased by and merged with Eastern Maine Healthcare Systems, owner of Eastern Maine Medical Center in Bangor, in 2013.