Marianne Liebmann net worth: Marianne Liebmann is one of seven remaining heirs to the Cargill/MacMillan fortune and has an estimated net worth of $3 billion dollars which makes her one of the richest people in Montana. Cargill, Inc. was founded by William Cargill in 1865, and grew from a grain storage company into a company dedicated to all services related to food production, from animal feed to storage. The company is the largest privately owned corporation in the United States, and has made the Cargills, and their extended family members, the MacMillans, into one of the richest families in the world. Marianne Liebmann, also known as Marianne Cargill Liebmann graduated from Montana State University, and currently lives in Bozeman, Montana. She is married, but does not reportedly have any children. Her exact wealth is unknown, as the owners of privately owned companies are not required to reveal their personal wealth, only the annual revenue of the company that they own.