Fonds consists largely of records created and collected by members of the Magrath family, including the Reverend James Magrath and his children, in the course of administering and occupying their farming estate (called Erindale) on the Credit River. Fonds includes correspondence, legal and financial records and ledgers, and plans of the estate and environs. There is also a small amount of material added to the fonds by later descendants of the family, including family histories and annotated transcriptions of the earliest Magrath correspondence.

The bulk of the correspondence consists of personal letters between family members, including James Magrath and his children, and most is written to Charles Magrath while on a trip to Ireland. Letters are largely concerned with family and personal affairs.

Note that the Magrath family correspondence includes occasional references to the activities of the First Nations (Mississauga Anishinaabe) people of the Credit area at that time referred to as the Credit Indians. The nature of these references is influenced by the perspective and prejudices of the Magraths.

The fonds comprises the following six series:

Series 1: Correspondence
Series 2: Legal records
Series 3: Financial records
Series 4: Family history records
Series 5: Erindale Estate maps and plans
Series 6: Transcriptions