John Armstrong was born on October 13, 1717 in Brookborough, County Fermanagh, Ireland, now a part of Northern Ireland. He was educated and became a civil engineer. Armstrong later immigrated to the United States as a surveyor for the Penn family, the colony proprietors at the time. As he plotted the land of what would become Carlisle, Pennsylvania, Armstrong became one of the area's first settlers and was appointed surveyor of Cumberland County. At the young age of 19 his surveying services were in high demand by all of the new settlers. Armstrong married Rebecca Lyon and they had two sons, James in 1748 and John Jr. in 1758.

During the French and Indian War Armstrong served as a Colonel in the Pennsylvania militia. At the time the village of Kittanning, derived from the Indian name Kit-Han-Ne [at the great river], was the central location for Indian raids on white settlements throughout western Pennsylvania in addition to parts of Virginia and Maryland. The defenseless Pennsylvania settlers lived in fear of "scalping parties," being burned at the stake, and violent raids. In June 1756, a collective force of Frenchmen and Delaware Indians attacked Fort Granville, near present day Lewistown, and took prisoners back to Kittanning, located along the Allegheny River. Armstrong's brother, Lieutenant Edward Armstrong, was among those killed in the raid.

On September 6, 1756, Armstrong led over 300 frontier troops on an expedition to reach Kittanning. His ranks included the future namesake of Potter County, James Potter, a militia lieutenant from Northumberland County who became a friend of Armstrong's. Thirty miles away from their destination, Armstrong and his troops rested on a white oak tree the night of the 6th, which was given the name "Armstrong's Oak" and stood until the early 1900's. As he proceeded toward the village of Kittanning on September 7, Armstrong sent ahead a troop after hearing of an Indian roadside campfire close to Kittanning. Fearing the Indians would gain information of his planned attack, he left the bulk of blankets, horses, and baggage with Lieutenant James Hogg and thirteen other men of his company to keep lookout for the enemy. Today, the location is known as "Blanket Hill."

On September 8, 1756, Colonel Armstrong bravely led his troops in an early morning attack on Kittanning. The troops' surprise attack during the Indians' sunrise dance ceremony successfully and brutally destroyed most of the village and killed over 30 Indian villagers. The Indian leader, Captain Jacobs, barricaded himself and family in his two-story log cabin which the Colonel ordered the troops to ignite. Using gunpowder to cause an explosion the troops followed orders and Captain Jacobs was shot as he jumped out of his window. In a 1927 article in the Western Pennsylvania Historical Magazine, J.W. King notes that Captain Jacobs' body was identified by his particular bob haircut called the "king's son" and a pouch found on his hip, one which he had received from a French officer in exchange for Lieutenant Armstrong's boots from Fort Granville. The sound of Captain Jacobs' cabin exploding was reportedly heard by French and Indian troops at Fort Duquesne (now Pittsburgh) who proceeded toward Kittanning but did not arrive at the battle site until the following day.

Including the bloody march back, in which Lieutenant Hogg and company were attacked at Blanket Hill, seventeen of Armstrong's men were Killed, thirteen wounded, and nineteen missing. Though Colonel Armstrong, who suffered a shoulder injury from a large musket ball during the battle, lost many of his troops by death or desertion, and though the prisoners were not successfully rescued, the attack was still considered a victory as the Indians receded from Kittanning and the raids lessened. Armstrong was named the "Hero of Kittanning" in addition to being warmly praised and presented with a medal by the city of Philadelphia where he traveled to collect the bounty money that had been placed on Captain Jacob. The "Kittanning Destroyed Medal" received by Armstrong was the first American decoration awarded for victory in battle. Today the victory is often called the Battle of Kittanning, the Armstrong Expedition, or the Kittanning Expedition. In the "History of Armstrong County," Robert Smith refers to appreciative notes exchanged by the city of Philadelphia and Colonel Armstrong:

"To Col. John Armstrong: Sir: The corporation of the city of Philadelphia greatly approve your conduct and public spirit in the late expedition against the town of Kittanning, and are highly pleased with the signal proofs of courage and personal bravery given by you and the officers under your command in demolishing that place. I am, therefore, ordered to return you and them the thanks of the Board for the eminent service you have thereby done your country. I am also ordered by the corporation to present you, out of their small public stock, with a piece of plate and silver medal, and each of your officers with a medal and a small sum of money, to be disposed of in a manner most agreeable to them; which the Board desire you will accept as a testimony of the regard they have for your merit. Signed by order, January 5, 1757. ATWOOD SHUTE, Mayor."

"To the Mayor, Recorder, Aldermen, and Common Council of the Corporation of the City of Philadelphia: GENTLEMEN: Your favor of the 5th instant, together with the medals and other genteel presents made to the officers of my battalion, by the corporation of the city of Philadelphia, I had the pleasure to receive by Capt. George Armstrong. The officers employed in the Kittanning expedition have been made acquainted with the distinguished honor you have done them, and desire to join with me in acknowledging it in the most public manner. The kind acceptance of our past services by the corporation gives us the highest pleasure and furnishes a fresh motive for exerting ourselves on every future occasion for the benefit of His Majesty's service in general and in defense of this province in particular. In behalf of the officers of my battalion, I have the honor to be, gentlemen, your most obedient and obliged humble servant, Carlisle, January 24, 1757. JOHN ARMSTRONG."

During the seven year French and Indian War, Colonel Armstrong went on to lead 2,700 Pennsylvania troops in the Forbes Expedition, the move that prompted the French to vacate and destroy Fort Duquesne, in 1758. During the expedition Armstrong became friends with a soon to be well known counterpart in the Virginia militia, Colonel George Washington.

The "Hero of Kittanning" entered the Revolutionary War as a brigadier general in the Pennsylvania militia in 1776 and was appointed to the same rank in the Continental Army by Congress in the same year. Armstrong shortly traveled to Charleston, South Carolina because his engineering skills were sought to help the defense of the Southern port. His skills paid off on June 28, 1776, when he led a collaborative effort of 500 frontier Continental riflemen, Pennsylvania militia, South Carolina militia, and General Lee's Virginia frontiersmen, in a successful effort to stop over 6,000 British troops from disembarking and invading at Charleston Harbor.

Armstrong then returned to Pennsylvania and was appointed Major General in the militia. He led his militia troops in the Battle of Brandywine as well as in the Battle of Germantown in 1777, after which he was given permission to end his duties on active command. Armstrong did go on, however, to represent Pennsylvania in the Continental Congress from 1779-1780. He also performed many civic duties in Cumberland County, including serving as county judge. Armstrong again represented Pennsylvania in the Continental Congress during the Articles of Confederation, 1787-1788.

Armstrong's sons followed in his footsteps politically as James Armstrong went on to become not only a physician, serving as a medical officer during the Revolutionary War, but also a U.S. Representative from Pennsylvania. John Armstrong Jr. became a Major in the Continental Army during the Revolutionary War as well as a Member of the Continental Congress. Armstrong died at his home in Carlisle, Pennsylvania on March 9, 1795. He was buried in Old Carlisle Cemetery. As J.W. King noted, Colonel John Armstrong was said to be by General James Wilkinson "The Hero of KittanningÄü?one of the most virtuous men who had lived in any age or country."

Armstrong County was formed March 12, 1800 from the three other counties of Allegheny, Lycoming, and Westmoreland and was named in honor of Colonel John Armstrong for his victory at Kittanning. Two "Hero of Kittanning" plaques exist today in Armstrong County, one outside Colonel Armstrong's former residence and the other outside of the Armstrong County Courthouse. A few miles southeast of Kittanning a "Blanket Hill" plaque also exists. In 2006 Armstrong County commemorated the 250th anniversary of the Battle of Kittanning with a reenactment that drew 5,000 people.