The National Park Service writes that Tilghman was even sick during his ride from Yorktown to Philadelphia "with chills and fever" and that he left the army in 1783 with failing health. In July 1775, the Second Continental Congress appointed him to one of the commissioners directed to make treaties with Indians along the frontier, seeking to ensure that they would remain neutral in the American Revolutionary War. In the summer of 1775, Tilghman became a lieutenant in the 3rd Battalion of the Philadelphia volunteer light infantry company commanded by Sharpe Dulaney. The company was integrated into the Continental Army in New Jersey in the Flying Camp military formation in June or July 1776. On August 8, 1776, he became one of the aides-de-camp to George Washington, the commander-in-chief of the Continental Army. During the Battle of Monmouth in 1778 and afterwards, Tilghman interpreted written and verbal communications between Washington, Lafayette, Von Steuben, and commanders of the Continental Army's French allies. On June 9, 1783, in St. Michael's Parish, Tilghman married Anna Maria Tilghman, his first cousin and daughter of Matthew Tilghman. Together they had two children: Anna Margaretta, born May 24, 1784, and Elizabeth Tench, born October 11, 1786. Tilghman was admitted as an original member of The Society of the Cincinnati of Maryland when it was established in November 1783. He died in Chestertown, Maryland, on April 18, 1786, at the age of 41.