John D. and Catherine T. MacArthur Foundation

The John D. and Catherine T. MacArthur Foundation is an American private foundation that makes grants and impact investments to support non-profit organizations in approximately 117 countries around the world. As of 2025, the MacArthur Foundation has an endowment of $9 billion and provides hundreds of millions of dollars annually in grants and impact investments. Based in Chicago, Illinois, it is one of the 20 largest private foundations in the United States. The foundation has awarded billions of dollars in grants since its first round of giving in 1978.