The first Coast Guard presence in the area was a Life Saving Station located on Little Cranberry Island, established by an act of congress on June 18th, 1878. In 1937, the Southwest Harbor complex was created and used as a lighthouse depot by the U.S. Light House Service. By 1945, the Coast Guard Station on Little Cranberry Island was moved to the facility in Southwest Harbor.
Mission requirements expanded from 1945 to 1966 and the CG 'Group' concept was established. The administrative and industrial building was completed in 1966 with a new barracks in 1968. The barracks was expanded and remodeled in 1984, then subequently renovated in July of 2006.
On June 30th, 2005 Group Southwest Harbor was recommissioned as a Sector Field Office (SFO), a sub-unit under CG Sector Northern New England, with it's own command and operational responsibility. Exactly one year later, in June of 2006, the SFO transitioned to a logistics and support department of CG Sector Northern New England.