The Breithaupt Hewetson Clark collection includes family papers the three families named; the Breithaupt family, the Hewetson family, and the Clark family. Made up of over several hundred cubic feet of archives, about 12,000 photographs, several thousand printed items and a large group of "subject and topical files" as well as plans, maps and drawings.

The largest set of family records are those related to the Breithaupt family of what is today Kitchener with the earliest documents being from the period of Liborious Breithaupt's emigration in 1843. A small group of family papers collected by Spencer Clark contains material on the Clark and Alexander families. Other families including the Devitt family of Waterloo and the Davis family of Brampton are also represented in the collection.

Also in the collection are records related to the Guild of All Arts (now the Guild Inn) in Scarborough, Ontario from its inception in 1932 to the 1980s. Founded by Rosa Breithaupt Hewetson Clark and Spencer Clark, the Guild began as a co-operative crafts community, and evolved primarily as a hotel and conference centre. In addition to Guild records, the Breithaupt Hewetson Clark collection holds smaller collections acquired by the Breithaupt family and by Spencer Clark. The personal library of Spencer Clark, which includes many books, periodicals, government documents, and ephemeral items, was donated together with the archival collections, and is particularly strong in the fields of urban planning, architecture, and Canadian art.