John Francis Mercer (1759-1821) was the son of John Mercer (1704-1768) of Marlborough in Stafford County, Virginia, and the half brother to George and James Mercer. He was commissioned a lieutenant in the 3d Virginia Regiment on 26 Feb. 1776, and served as one of the Virginia delegates to Congress in 1784. On 3 February 1785, Mercer married Sophia Sprigg (1766–1812), the eldest daughter of Richard Sprigg of Annapolis. That same year, Mercer took over from his brother, James Mercer, the management of the debt-ridden estate of their father, John Mercer (d. 1768), the attorney who handled the first settlement of Daniel Parke Custis’s estate in 1761 after GW’s marriage to Custis’s widow. John Francis Mercer  was also a Republican member of Congress from Maryland and a native of Fredericksburg.