John Mercer, Gentleman, (February 6, 1704/5 - October 14, 1768), prominent attorney-at-law, lived at Marlborough which had been the county seat of Stafford County 1691-1718. The planned port of entry at the Town of Marlborough was not a success and Mercer, after gaining title to all the town lots and a considerable acreage adjoining in Potomac Neck, established himself there. He married first on June 10, 1725 Catherine Mason (June 21, 1707-June 15, 1750) only child of Colonel George Mason (16??-1716) and his second wife Elizabeth Waugh, daughter of the Reverend Mr. John Waugh. About 1744 Mercer began construction of a handsome brick residence at Marlborough and here, his journal and account books indicate, he lived in the height of style. Mercer married secondly on November 10, 1750 Ann Roy (17??-1770), daughter of Doctor Mungo Roy of Essex County. John Mercer had a large family concerning whom considerable has been written. There is a detailed account of his family in The Virginia Genealogist, Volume 3, page 99 et seq.