Henry Dearborn (February 23, 1751 – June 6, 1829) was an American military officer and politician. In the Revolutionary War, he served under Benedict Arnold in his expedition to Quebec, of which his journal provides an important record. After being captured and exchanged, he served in George Washington's Continental Army. He was present at the British surrender at Yorktown. Dearborn served on General George Washington's staff in Virginia.

He served as Secretary of War under President Thomas Jefferson, from 1801 to 1809, and served as a commanding general in the War of 1812. In later life, his criticism of General Israel Putnam's performance at the Battle of Bunker Hill caused a major controversy. Fort Dearborn and Dearborn Park in Illinois, Dearborn County, Indiana, and Dearborn, Michigan, were named in his honor.

Henry Dearborn was born February 23, 1751, to Simon Dearborn and Sarah Marston in North Hampton in the Province of New Hampshire. He was descended from Godfrey Dearborn, from Exeter in England, who came to the Massachusetts Bay Colony in 1639. Godfrey Dearborn settled first at Exeter, New Hampshire, and soon after at Hampton, where four successive generations of his descendants lived. Henry spent much of his youth in Epping, where he attended public schools. He grew up as an athletic boy, notably strong and a champion wrestler. He studied medicine under Dr. Hall Jackson of Portsmouth and opened a practice on the square in Nottingham, New Hampshire, in 1772.

Dearborn was married three times: to Mary Bartlett in 1771, to Dorcas (Osgood) Marble in 1780, and to Sarah Bowdoin, widow of James Bowdoin, in 1813. Henry Alexander Scammell Dearborn was his son by his second wife.

When fighting in the American Revolutionary War began, Dearborn fought with the Continental Army as a captain in the 1st and 3rd New Hampshire Regiments; he soon rose to the rank of lieutenant colonel. He was appointed Deputy Quartermaster General in July 1781 and served on George Washington's staff while in Virginia. At age twenty-three, he organized and led a local militia troop of sixty men to the Boston area, where he fought on June 17, 1775, at the Battle of Bunker Hill as a captain in Colonel John Stark's 1st New Hampshire Regiment. During the battle, Dearborn observed that "Not an officer or soldier of the continental troops engaged was in uniform, but were in the plain and ordinary dress of citizens; nor was there an officer on horseback." Dearborn years later would accuse Israel Putnam of failing his duty during that battle, resulting in what has since been known as the Dearborn-Putnam controversy.

Dearborn volunteered to serve under Colonel Benedict Arnold in September 1775, during the difficult American expedition to Quebec. Later Dearborn would record in his Revolutionary War journal their overall situation and condition: "We were small indeed to think of entering a place like Quebec. But being now almost out of provisions we were sure to die if we attempted to return back and we could be in no worse situation if we proceeded on our rout."

On the final leg of the march, Dearborn was taken seriously ill with fever, forcing him to remain behind in a cottage on the Chaudière River. Later, he rejoined the combined forces of Arnold and Gen. Richard Montgomery in time to take part in the assault on Quebec. Dearborn's journal is an important record for that campaign. During the march he and Aaron Burr became companions. Along with a number of other officers, Dearborn was captured on December 31, 1775, during the Battle of Quebec, and detained for a year. He was released on parole in May 1776, but he was not exchanged until March 1777.

After fighting at Ticonderoga in July 1777, Dearborn was appointed major in the regiment commanded by Alexander Scammell.