The Harold K.L. Castle Foundation was founded in 1962 by Harold K.L. Castle. Upon his death in 1967, Mr. Castle bequeathed a sizeable portion of his real estate assets to the Foundation. These assets are the base from which the Foundation's grants are made. Harold Castle's son, James C. Castle, was a director of the Foundation since its inception, and succeeded Harold Castle as president in 1968. He held this position until his death in 1994. In 1994, Harold Castle's grandson, James C. McIntosh, was elected President. Directors John C. Baldwin and James C. McIntosh are grandsons of Harold and Alice Castle.
The Foundation is the largest private foundation based in Hawaii.