William Larimer Mellon [1868-1949] was the grandson of Irish immigrant Thomas Mellon [1813-1908] and his wife Sarah Jane Negley [1817-1909]. Thomas Mellon came to America in 1818 with his parents, who settled in Pittsburgh, and through his entrepreneurial skills and fortuitous investments became a very wealthy and powerful man with a career as a lawyer and later a judge, and a banker. Thomas had four sons: Thomas Alexander [1844-1899], James Ross [1846-1934], Andrew William [1855-1937], and Richard Beatty [1858-1933]. William Larimer Mellon was the son of James Ross Mellon and his wife Rachel Hughey Larimer. William Larimer Mellon married Mary Hill Taylor [1872-1942], with whom he had four children: Matthew Taylor [b. 1897], Rachel Larimer [b. 1899], Margaret [b. 1901] and William Larimer, Jr. [b. 1910]. The Mellon family is known for its commercial and banking fortunes and its philanthropy. Andrew W. Mellon was the founder of the National Gallery of Art.
Koskoff, David E. The Mellons: The Chronicle of America's Richest Family. New York, 1978.