The Thornhill Historical Foundation has a relationship (formal or informal) with the following organizations:
- Ontario Historical Society
This is the legal "parent" of all historical organizations in Ontario. It is a not-for-profit charity which receives some finalcial support from the Ontario Government.
- Ontario Heritage Trust
This is the Province's lead heritage agency.
- Society for the Preservation of Historic Thornhill (SPOHT)
SPOHT is a not-for profit organization charged with preserving the surviving remnants of 19th Century and early 20th Century Thornhill.
- City of Vaughan
The Robert West house is within the City of Vaughan. The City plays a role is designating properties within its boundaries as having historical value.
- City of Markham
The Foundation has no formal relationship with the City of Markham however; there is an informal relationship given that a portion of Thornhill exists within Markham; and, the Robert West House faces onto Markham from the west side of Yonge Street.
Letter of Good Standing From Ontario Historical Society