1George Mercer to Robert Johnston, 26 December 1755 (Washington Papers)
Mr. Johnston was probably the Robert Johnston (d. 1763) who appeared before the Frederick County court on 6 Jan. 1756 to take his oath along with Surgeon James Roy, also a volunteer, and a number of other officers of the Virginia Regiment. Robert Johnston was later a surgeon in the Virginia Regiment under Col. William Byrd III.