Smith College has recently published online finding aids to two collections.
Sylvia Plath collection, ca.approximately 1930-1998
Collection number: MRBC.MS.00045
Abstract: The Sylvia Plath collection contains writings by and about the American poet, novelist, and Smith College graduate, including poems, journals, articles, and correspondence to and from Plath. The bulk of the collection is manuscript, printed, or published materials but also includes realia, and audio/visual materials.
The collection is held by the Mortimer Rare Collection in the Neilson Library. Currently the library is under construction so the collection is accessible in the Young Library, 4 Tyler Drive.
The second collection is the papers of Plath's psychiatrist, Ruth Barnhouse (a.k.a. Ruth Beuscher).
Ruth Tiffany Barnhouse papers, 1915-1999, 2008
Collection number: SSC.MS.00202
Abstract: Ruth Tiffany Barnhouse was a psychiatrist, theologian, and ordained Episcopal priest known for being poet Sylvia Plath's psychiatrist, and for her theological publications related to homosexuality, sex, and women in the Christian church. This collection contains materials reflecting both her personal and professional lives, most of it from about 1970 and later. The collection contains a small amount of materials related to Sylvia Plath, which have been put in separate series for ease of access and reference.
The Barnhouse papers are held by the Sophia Smith Collection which is also temporary located in the Tyler Library.
It's simply fantastic that this resource is now available online.
The Special Collections website should have all the information you need if planning to visit. These finding aids are now listed on the Archival Materials page of A celebration, this is.
All links accessed 12 September 2018.