Elizabeth Jefferson(1744-1774), was Thomas Jefferson's younger sister; he appears to have used the nickname "Bet" for her. Of her brief life very little is known. Tradition holds she was mentally deficient. This information comes primarily from a letter of family intimate Wilson Miles Cary to Jefferson's great-granddaughter, Sarah N. Randolph in which he writes, "I have always understood that she was very feeble minded if not an idiot - that she and her maid were drowned together while attempting to cross the Rivanna in a skiff." The bare details of Elizabeth's death recorded in Jefferson's Memorandum Books neither confirm nor deny Cary's history. In the year 1774, Jefferson entered: "Mar. 1. My sister Elizabeth was found last Thursday being Feb. 24...Mar. 7. Sold my two old book cases to Mr. Clay for 5. of which credit him 40/ for performing the funeral service this day on burying my sister Elizabeth, & 40/ more for preaching Mr. Carr's funeral sermon...Mar 10. Took admn. of E. Jefferson's estate."
In age Elizabeth was the sibling closest to Jefferson. The family Prayer Book tells us that she was born on November 4, 1744, never married, and according to the entry believed in Jefferson's hand, died January 1, 1773. If this latter entry were made by Jefferson, it obviously contradicts his memorandum book notes and could have been made much later. (The death date recorded in the Memorandum Books is presumed to be the correct one.) Page Smith, author of Jefferson, A Revealing Biography, maintains that an earthquake that shook Monticello on February 21, 1774 was the cause of Elizabeth Jefferson's running away and subsequent death. There were some natural phenomena occurring at this time, and indeed, on February 21, 1774 Jefferson records in his Memorandum Book an earthquake that, "...shook the houses so sensibly that every body run out of doors." An aftershock was felt again the following afternoon on February 22, two days before Elizabeth was found. During this period there may have been heavy precipitation as well, for on March 6, the day before Elizabeth's funeral, Jefferson notes, "A flood in the Rivanna 18 I. higher than the one which carried N. Lewis's bridge away & that was the highest ever known except the great fresh in May 1771." Unfortunately, Jefferson's surviving meteorological diaries date only to July 1776, so we have no record of how cold the temperatures may have been at Monticello during these February/March days. These events create interesting speculations but cannot be positively linked as causal in Elizabeth Jefferson's death. Her death as her life remain surrounded by many unanswerable questions.