Lucy was the daughter of Thomas Flucker, a royalist in Boston, Massachusetts. Lucy incurred her father's displeasure when she married the young bookseller, Henry Knox, a man in trade. After the battle of Lexington, Lucy's family returned to England, leaving the ardent young patriots in the war torn colonies. Boston at that time became a prison to its residents as General Gage refused to let the citizens leave to join the patriot army. Major Knox escaped to Cambridge and Lucy joined him later, bringing his sword, which she had quilted into the lining of her cloak. That set the pattern for their lives during the war years. From Bunker Hill to Yorktown, she remained as close to her husband as possible throughout the campaigns.

Major Knox was soon appointed to General George Washington's staff. Lucy and Mrs. Washington were at Valley Forge during that bitter winter where they devoted their time to sewing, mending, and attending the sick at the encampment. Lucy was with Mrs. Washington at Mount Vernon during the siege of Yorktown. Later her husband served his country as President Washington's Secretary of War. Lucy was described as "a woman of much tact, quick and ready sympathy and good judgment, combined with great good-nature and a love of fun."

The Knox's retired to Maine after the General's service in the War Office. Lucy died in June 1824, at the age of 68, having outlived her husband by 18 years. (From "The Pioneer Mothers of America," H.C. and M.W. Green, Putnam and Sons, New York.1912.)