Further reading:

J. Elliott Drinard, “James Mercer, 1736-1793,” Proceedings of the Thirty-Ninth Annual Meeting of the Virginia State Bar Association (August 1928), 423-435.

John Melville Jennings and James Mercer, “Letters of James Mercer to John Francis Mercer,” The Virginia Magazine of History and Biography, Vol. 59, No. 1 (Jan. 1951); and Vol. 59, No. 2 (April 1951); 13 letters, January-September 1783.
James Mercer’s letters to his half-brother, John Francis Mercer, while John Mercer was attending the Continental Congress in 1782.

Research collections:

Founders Online, from the National Archives and Records Administration, provides access to Mercer’s correspondence, 1771-1793, in the Papers of George Washington and the Papers of Thomas Jefferson; most concern Washington’s efforts to collect money owed to him by Mercer. Of note are a Petition to Governor and Council (November 1, 1771) concerning distribution of bounties for service in the French and Indian War; a Notice Concerning Legal Fees  (May 20, 1773) a complaint from Mercer and five other attorneys practicing in the General Court; and a letter to Governor Thomas Jefferson pleading for protection of the gunworks in Fredericksburg.

University of Virginia (Albert and Shirley Small Special Collections Library)
Charlottesville, Va.
Legal notes of Charles Lee, 1783-1793,1855; 1 volume (microfilm; originals privately owned).
Notes regarding opinions of Mercer and other judges of the General Court and the Virginia Court of Appeals.