Betty Duvall (1845–1891) was a Confederate spy during the American Civil War. Betty Duvall was from Washington, D.C. She was the daughter of Eli Duvall Sr. and Sarah (née Thompson) Duvall. Washington D.C.-based spy Rose O'Neal Greenhow gave her a note about a Union plan for the first Battle of Manassas (or Bull Run) to give to General P. G. T. Beauregard; Duvall carried it tucked in her hair. She continued to be a spy, and for one of her missions she brought her cousin. She was descended from the immigrant Mareen Duvall.