MERCER, John Francis, statesman, born in Stafford county, Virginia, 17 May, 1759; died in Philadelphia, Pennsylvania, 30 August, 1821. He was graduated at William and Mary collage in 1775, entered the 3d Virginia regiment as lieutenant in 1776, became captain in 1777, and was aide to General Charles Lee till the battle of Monmouth, when his sympathy with that officer in his disgrace induced him to resign from the army. He returned to Virginia, but soon afterward raised and equipped, at his own expense, a troop of horse, of which he was commissioned lieutenant-colonel, and, joining General Robert Lawson's brigade, he served with it, at Guilford and elsewhere until it was disbanded. He then attached his command to the forces under Lafayette, with whom he remained until the surrender at Yorktown. After the war he studied law with Thomas Jefferson, and from 1782 till 1785 was a delegate from Virginia to the Continental congress. He married Sophie, daughter of Richard Sprigg, of West River, Maryland, in 1785, removed to " Cedar Park," his wife's estate, and soon became a leader in Maryland polities. He was a delegate to the convention that framed the United States constitution, but opposed the plan that was adopted, and withdrew without signing the document. He was in congress in 1792-'4, served in the legislature for several years, was governor of Maryland in 1801-'3, and after several years of retirement was again in the legislature. Governor Mercer was the trusted personal and political friend of Jefferson. He died while on a visit to Philadelphia for medical advice. --His daughter, Margaret, born in Annapolis, Maryland, in 1792; died in Virginia in June, 1846, voluntarily reduced herself from affluence to poverty by freeing her slaves and sending them to Liberia, and she subsequently taught for twenty years in Virginia. She prepared two volumes for her pupils, " Studies for Bible Classes " and " Ethics, a Series of Lectures to Young Ladies." See memoir of her, by Caspar Morris (Philadelphia, 1848).