Ledyard was in command of Fort Trumbull and Fort Griswold on September 6, 1781, when Fort Griswold fell to the British under Benedict Arnold in the Battle of Groton Heights. Ledyard had refused a British demand to surrender the fort.
Ledyard resisted the attack of a British force of 800 men led by Lieutenant Colonel Eyre for nearly an hour, with 157 hastily collected and poorly armed militia inside Fort Griswold, according to American accounts of the battle. This attack was made on three sides; there was a battery between the fort and the river, but the Americans could spare no men to work it. The British made their way into the fosse and scaled the works in the face of severe fire from the garrison. Eyre was wounded and died twelve hours afterward on shipboard, and his successor Major Montgomery was killed while mounting the parapet. The command devolved upon Tory Major Bromfield, who effected an entrance into the fort after nearly 200 of his men had been disabled, including 48 killed, the Americans having lost only about twelve men.
After the British stormed Fort Griswold, according to American accounts written in the mid-19th century, Ledyard ordered his men to cease firing and to lay down their arms. Bromfield demanded to know who commanded the fort. Ledyard allegedly replied, "I did, sir, but you do now," and offered his sword. The British officer took the sword and stabbed Ledyard to death, initiating a massacre of some eighty captive Americans.
Arnold wrote the following account of the battle in a despatch to Henry Clinton two days afterward: “I have inclosed a return of the killed and wounded, by which your excellency will observe that our loss, though very considerable, is short of the enemy's, who lost most of their officers, among whom was their commander, Col. Ledyard. Eighty-five men were found dead in Fort Griswold, and sixty wounded, most of them mortally. Their loss on the opposite side (New London) must have been considerable, but cannot be ascertained.”
William Ledyard's nephew was noted explorer John Ledyard.
- One or more of the preceding sentences incorporates text from a publication now in the public domain: Wilson, James Grant; Fiske, John, eds. (1892). "Ledyard, William". Appletons' Cyclopædia of American Biography. New York: D. Appleton.
- Zug, James (6 March 2009). American Traveler: The Life and Adventures of John Ledyard, the Man Who Dreamed of Walking the World. Basic Books. p. 272. ISBN 978-0-7867-3941-7.
- Ledyard's service record from Francis B. Heitman's Historical Register of Officers of the Continental Army
- "The Coming of the Revolution 1773-1776", Connecticut Society of the Sons of the American Revolution
- Joseph Duffy, "Connecticut At War", Connecticut Humanities Council
- Ledyard genealogy page (source for birthdate)
- Columbia Encyclopedia entry