On 14 August 1788, William married Mary Johnson d'Evelin, a wealthy Irish widow with children. William's son, Temple, after a failed business career in the U.S., lived with his father and stepmother for a time, and followed in his grandfather and father's footsteps and had an illegitimate daughter, Ellen (15 May 1798 London – 1875 Nice, France), with Ellen Johnson d'Evelin, the sister-in-law of his stepmother, Mary. William took responsibility for his granddaughter Ellen. Temple moved to Paris, where he lived the remainder of his life and never saw his father again. After Mary died in 1811, William continued to live with Ellen, age 13 at the time, and when he died in 1813 he left most of his small estate to her.