son of William and Sarah (Earwicker) Hillyer. William, Jr. was brought
to the United States at age four, and in 1822 his family settled in New
He was taught the trade of carpentry by his father, but in his youth his love for art blossomed, and in his teen years he was already busy sketching the portraits of his Lower Manhattan neighbors. From the 1830s to the 1860s, Hillyer worked from a variety of portraiture studios he operated in his neighborhood. He apparently also worked for some time in Philadelphia.
He married Mary Gumbs in New York City, about 1835, and the couple had several children. By 1870, William, Jr. had moved his family to Champaign, Illinois, where he bought a farm and spent the remainder of his life. It is believed that he continued painting until his death in 1904, but for the last three decades of his life, his main occupation was farming. He and his wife
are buried in the Mt. Hope Cemetery, Champagne, Illinois.