Andrew Mellon"s family was composed of entrepreneurs who had accumulated wealth through the companies that they owned. According to the United States department of the Treasury, Andrew Mellon showed an acumen for finance when he formed a lumber business when he was only 17 (History of the Treasury). Mellon joined his father"s banking firm at the age of 19 and became the owner of that bank at the age of 27 (History of the Treasury). In addition, Mellon aided in organizing the Union Trust Company and Union Savings Bank of Pittsburgh. As a young adult, Mellon also built personal wealth in the steel, oil, shipbuilding, and construction industries (History of the Treasury). Throughout World War I Mellon was also involved in the National War Council of the YMCA the American Red Cross, The National Research council of Washington and the Executive Committee of the Pennsylvania State Council of National Defense (History of the Treasury). .

             By the time Andrew Mellon became Secretary of State many of the corporations that the family had interests in had amassed for the family Billions of dollars. Most of this fortune came from the banking, coal and steal industries. In fact .

             "In but four corporations and four banks, the majority of whose income flowed into the family's pockets, dividends soared from a mere $6,950,000 in 1920 to $24,686,000 eight years later.Assets of four of the family's firms rose--between the inaugurations of Harding and Hoover--from $428,000,000 to $952,000,000. These figures did not include Standard Steel Car and McClintic-Marshall whose financial reports were made known only to their few stockholders, and Pittsburgh Coal, Pittsburgh Plate Glass, Crucible Steel, in which the family held large blocks of stocks and bonds. Money on deposit in the Mellons' four largest banks advanced in that period from $229,000,000 to $351,000,000. The Pittsburgh bankers indisputably were a billionaire family (O'Connor).