The municipal history of Harmony Township began on April 3, 1851, when it was formed by an Act of the Legislature out of Economy Township. It included the village of Economy which was the home of the Harmony Society.
It was here that the Indian village of Logstown was located. The Indian name for the town was "Maugh-wa-wame" meaning broad plains or plateaus. Conrad Weiser and George Croghan signed the Treaty of Logstown with the Delaware, Shawnee, and Wyandot Indians in 1748, laying the basis of the English claim to the Ohio-Allegheny country. That this resulted in French counterclaims leading to the French and Indian War is only another way of saying that it was an attempt (ultimately successful) to save the Ohio Valley for the English-speaking people.
It was also at Logstown that the Reverend Joseph Peter Bonnecamps, a member of the Society of Jesus, performed the first public religious ceremony (a Catholic mass) in what is now Beaver County on the morning of August 9, 1749. Reverend Bonnecamps was chaplain to the French explorer Celeron de Blainville who was sent by the governor-general of all New France to expel the English traders from this region and to assert the French claim. To assert the English claims to the Ohio Valley, Virginia's Lieutenant-Governor, Robert Dinwiddie, sent George Washington to the French Fort LeBoeuf in the fall of 1753. Washington reached Logstown on November 26, conferred with local Indian leaders, and then pushed on to Fort LeBoeuf.
The year following Washington's visit to Logstown saw French and English armies and traders pass through the area, forcing the Indians to abandon the area by 1758. Colonel Henry Bouquet, in an expedition against the Ohio Indians, passed through the area and clearly located the remnants of Logstown on the north bank of the Ohio. After the American Revolution, Harmony Township was part of the Depreciation Lands and was surveyed by Daniel Leet in 1785. Issac Melcher (or Melchior) of Philadelphia acquired the site of Logstown in 1787 and laid out the plans for the town of Montmorin, but they were never carried out.
In the fall of 1792, the Logstown area of Harmony Township once again became the center of great activity. Major General Anthony Wayne, who had been asked by President Washington to organize and command an army against the Indians in the Northwest Territory, moved his troops from Pittsburgh in November, 1792, to a site just north of the old Indian village which he named "Legionville." During the winter and early spring of 1792-93, General Wayne molded his Legion of the United States into the first disciplined, efficient military unit of the United States Army under the present Constitution.
There was one more important chapter in the history of Harmony Township. In 1824, Father George Rapp, leader of a band of religious pietists known as the Harmony Society, purchased over 3,000 acres of land for the third and last home of the Society which he called Economy. Three years later, Economy Township, including the Harmonist lands, was formed out of New Sewickley Township. Then, in 1851, Harmony Township, consisting almost exclusively of Harmonist lands, was formed from Economy. The site of Economy village was lost in 1905, when Ambridge was incorporated from Harmony Township.
The community experienced its greatest growth following World War II as a result of a large number of residents from Ambridge and surrounding areas seeking a quiet escape from the more industrialized areas of the County.