Anna Scott Jefferson Marks
From Thomas Jefferson Encyclopedia
Anna Scott Jefferson, Thomas Jefferson's youngest sister, was born October 1, 1755 (a twin to Randolph Jefferson) and married Hastings Marks in October 1787, according to Peter Jefferson's prayer book. Unfortunately there doesn't seem to be one single good source on Anna (or Anne, as she was also sometimes referred to). There is a note in our files on her that she and Hastings had one son, Valentine, who married a "Miss Brockenbough of 'Port Royal.' (this is according to a letter from Martha Jefferson Trist Burke to Jefferson Taylor, 1902). Anna (or Anne) Scott Marks (called "Aunt Marks" by TJ's children and grandchildren) came to live at Monticello with her brother after her husband's death in 1811; she herself died on July 8, 1828.
Boyd, Julian, ed., The Papers of Thomas Jefferson (Princeton: Princeton University Press, 1950-)
Looney, J. Jefferson, ed., The Papers of Thomas Jefferson: Retirement Series (Princeton: Princeton University Press, 2004-)
Bear, James A. and Lucia C. Stanton, eds., Jefferson's Memorandum Books (Princeton: Princeton University Press, 1997)
Family Letters Project: http://familyletters.dataformat.com