The McLean Foundation was established in 1945 by James Stanley (J.S.) McLean and is one of the oldest private family foundations in Canada. J.S. and his wife, Edith, were avid supporters of numerous charitable causes, particularly in the areas of social welfare, education, environmental conservation and the arts. They were also avid art collectors, most notably of works by the Group of Seven and other Canadian artists such as Tom Thomson, David Milne and Emily Carr.

The Foundation was initially financed through gifts and bequests by J.S. and Edith McLean totalling more than $1.7 million. Edith McLean also made gifts and bequest to the Foundation, to a total value of approximately $450 000. Mr. William F. McLean, Mrs. Mary F. Stewart, and Mrs. Carol June McLean made bequests to the Foundation in their wills in 2001, 2009 and 2021, respectively. By 2025, the endowment stood at approximately CDN $68 million. Since its inception, four generations of family members, together with several external advisors, have dedicated their time, energy, and expertise to leading and stewarding the growth of the Foundation.

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Over a period of nearly 80 years, the Foundation has supported organizations representing a wide variety of interests, in line with its stated mandate:

To maintain a flexible policy, with particular emphasis on projects showing promise of general social benefit but which may initially lack broad public appeal.

Recognizing the urgent threat of climate change, in 2023, the Foundation's Board of Directors decided to dedicate at least 20% of its granting budget to climate action projects. The Foundation also continues to fund extensively in the areas of social welfare, health, education and the arts.