Pennsylvania /ˌpɛnsɨlˈveɪnjə/, officially the Commonwealth of Pennsylvania, is a US state that is located in the Northeastern and Mid-Atlantic regions of the United States, and the Great Lakes region. The state borders Delaware to the southeast, Maryland to the south, West Virginia to the southwest, Ohio to the west, Lake Erie and Ontario, Canada to the northwest, New York to the north and New Jersey to the east. The Appalachian Mountains run through the middle of the state.

Pennsylvania is the 33rd most extensive, the 6th most populous, and the 9th most densely populated of the 50 United States. The state's four most populous cities are Philadelphia, Pittsburgh, Allentown, and Erie. The state capital is Harrisburg. Pennsylvania has 51 miles (82 km) of coastline along Lake Erie and 57 miles (92 km) of shoreline along the Delaware Estuary. The state is one of the 13 original founding states of the U.S.

Before the Commonwealth was settled by Europeans, the area was home to the Delaware (also known as Lenni Lenape), Susquehannock, Iroquois, Eriez, Shawnee, and other American Indian Nations. Both the Dutch and the English claimed both sides of the Delaware River as part of their colonial lands in America. The Dutch were the first to take possession, which has impact on the history of Pennsylvania.

By June 3, 1631, the Dutch had started the settlement of the Delmarva Peninsula by establishing the Zwaanendael Colony on the site of present-day Lewes, Delaware. In 1638, Sweden heated up the issue by establishing the New Sweden Colony, centered on Fort Christina, on the site of present-day Wilmington, Delaware. New Sweden claimed and, for the most part, controlled the lower Delaware River region (Parts of present Delaware, New Jersey and Pennsylvania) but settled few colonists there.

On March 12, 1664, King Charles II of England gave James, Duke of York a grant that included all of the lands included in the original Virginia Company of Plymouth Grant as well as other lands. This grant was – again – in conflict with the Dutch claim for New Netherland, which included parts of today's Pennsylvania.

On June 24, 1664, The Duke of York sold the portion of his large grant that included present day New Jersey to John Berkeley and George Carteret for a proprietary colony. The land was not yet in British possession, but the sale boxed in the portion of New Netherland on the West side of the Delaware River. The British conquest of New Netherland was commenced on August 29, 1664, when New Amsterdam was coerced to surrender, facing the cannons on British ships in New York Harbor. This conquest continued, and was completed in October 1664, when the British captured Fort Casimir in what today is New Castle, Delaware.

The Peace of Breda between England, France and the Netherlands confirmed the British conquest on July 21, 1667, although there were temporary reversions.

On September 12, 1672, as part of the Third Anglo-Dutch War, the Dutch re-conquered New York Colony/New Amsterdam, the Dutch established three County Courts which went on to become original Counties in present-day Delaware and Pennsylvania. The one that later transferred to Pennsylvania was Upland. This was partially reversed on February 9, 1674, when the Treaty of Westminster ended the Third Anglo-Dutch War, and reverted all political situations to the status quo ante bellum. The British retained the Dutch Counties with their Dutch names. By June 11, 1674, New York reasserted control over the outlying colonies, including Upland, but the names started to be changed to British names by November 11, 1674. Upland was partitioned on November 12, 1674, producing the general outline of the current border between Pennsylvania and Delaware.

On February 28, 1681, Charles II granted a land charter to William Penn to repay a debt of £16,000 (around £2,100,000 in 2008, adjusting for retail inflation) owed to William's father, Admiral William Penn. This was one of the largest land grants to an individual in history. The King named it Pennsylvania in honor of William Penn. Penn, who originally called it New Wales, then Sylvania, was embarrassed at the change, fearing that people would think he had named it after himself, but King Charles would not rename the grant. Penn established a government with two innovations that were much copied in the New World: the county commission and freedom of religious conviction.

What had been Upland on what became the Pennsylvania side of the Pennsylvania-Delaware Border was renamed as Chester County when Pennsylvania instituted their colonial governments on March 4, 1681. The Quaker leader William Penn had signed a peace treaty with Tammany, leader of the Delaware tribe, beginning a long period of friendly relations between the Quakers and the Indians. Additional treaties between Quakers and other tribes followed. The treaty of William Penn was never violated.

18th century

Between 1730 and when it was shut down by Parliament with the Currency Act of 1764, the Pennsylvania Colony made its own paper money to account for the shortage of actual gold and silver. The paper money was called Colonial Scrip. The Colony issued "bills of credit", which were as good as gold or silver coins because of their legal tender status. Since they were issued by the government and not a banking institution, it was an interest-free proposition, largely defraying the expense of the government and therefore taxation of the people. It also promoted general employment and prosperity, since the Government used discretion and did not issue too much to inflate the currency. Benjamin Franklin had a hand in creating this currency, of which he said its utility was never to be disputed, and it also met with the "cautious approval" of Adam Smith.

James Smith wrote that in 1763, "the Indians again commenced hostilities, and were busily engaged in killing and scalping the frontier inhabitants in various parts of Pennsylvania." Further, "This state was then a Quaker government, and at the first of this war the frontiers received no assistance from the state." The ensuing hostilities became known as Pontiac's War.

After the Stamp Act Congress of 1765, Delegate John Dickinson of Philadelphia wrote the Declaration of Rights and Grievances. The Congress was the first meeting of the Thirteen Colonies, called at the request of the Massachusetts Assembly, but only nine colonies sent delegates. Dickinson then wrote Letters from a Farmer in Pennsylvania, To the Inhabitants of the British Colonies, which were published in the Pennsylvania Chronicle between December 2, 1767, and February 15, 1768.

When the Founding Fathers of the United States convened in Philadelphia in 1774, 12 colonies sent representatives to the First Continental Congress. The Second Continental Congress, which also met in Philadelphia (in May 1775), drew up and signed the Declaration of Independence in Philadelphia, but when that city was captured by the British, the Continental Congress escaped westward, meeting at the Lancaster courthouse on Saturday, September 27, 1777, and then to York. There they and its primary author, John Dickinson, drew up the Articles of Confederation that formed 13 independent colonies into a new nation. Later, the Constitution was written, and Philadelphia was once again chosen to be cradle to the new American Nation.

Pennsylvania became the second state to ratify the U.S. Constitution on December 12, 1787, five days after Delaware became the first.

Dickinson College of Carlisle was the first college founded in the United States. Established in 1773, the college was ratified five days after the Treaty of Paris on September 9, 1783. The school was founded by Benjamin Rush and named after John Dickinson.

For half a century, the Commonwealth's General Assembly (legislature) met at various places in the general Philadelphia area before starting to meet regularly in Independence Hall in Philadelphia for 63 years. But it needed a more central location, as for example the Paxton Boys massacres of 1763 had made the legislature aware. So, in 1799 the General Assembly moved to the Lancaster Courthouse, and finally in 1812 to Harrisburg.

The General Assembly met in the old Dauphin County Court House until December 1821, when the Federal-style "Hills Capitol" (named for its builder, Stephen Hills, a Lancaster architect) was constructed on a hilltop land grant of four acres set aside for a seat of state government by the prescient, entrepreneurial son and namesake of John Harris, Sr., a Yorkshire native who had founded a trading post in 1705 and ferry (1733) on the east shore of the Susquehanna River. The Hills Capitol burned down on February 2, 1897, during a heavy snowstorm, presumably because of a faulty flue. The General Assembly met at Grace Methodist Church on State Street (still standing) until a new capitol could be built. Following an architectural selection contest that many alleged had been "rigged," Chicago architect Henry Ives Cobb was charged with designing and building a replacement building; however, the legislature had little money to allocate to the project, and a roughly finished, somewhat industrial building (the Cobb Capitol) was completed. The General Assembly refused to occupy the building. Political and popular indignation in 1901 prompted a second contest that was restricted to Pennsylvania architects, and Joseph Miller Huston of Philadelphia was chosen to design the present Pennsylvania State Capitol that incorporated Cobb's building into magnificent public work finished and dedicated in 1907.

The new state Capitol drew rave reviews. Its dome was inspired by the domes of St. Peter's Basilica in Rome and the United States Capitol. President Theodore Roosevelt called it "the most beautiful state Capital in the nation" and said, "It's the handsomest building I ever saw" at the dedication. In 1989, The New York Times praised it as "grand, even awesome at moments, but it is also a working building, accessible to citizens ... a building that connects with the reality of daily life".

Pennsylvania accounts for nine percent of wooded areas in the United States. In 1923 President Calvin Coolidge established the Allegheny National Forest under the authority of the Weeks Act of 1911 in the northwest part of the state in Elk, Forest, McKean, and Warren Counties for the purposes of timber production and watershed protection in the Allegheny River basin. The Allegheny is the state's only national forest.

James Buchanan, of Franklin County, the only bachelor President of the United States, was the only one to be born in Pennsylvania. The Battle of Gettysburg—the major turning point of the Civil War—took place near Gettysburg. An estimated 350,000 Pennsylvanians served in the Union Army forces including 8,600 African American military volunteers.

Pennsylvania was also the home of the first commercially drilled oil well. In 1859, near Titusville, Pennsylvania, Edwin Drake successfully drilled the well, which led to the first major oil boom in United States history.

Pennsylvania is 170 miles (274 km) north to south and 283 miles (455 km) east to west. Of a total 46,055 square miles (119,282 km²), 44,817 square miles (116,075 km²) are land, 490 square miles (1,269 km²) are inland waters, and 749 square miles (1,940 km²) are waters in Lake Erie. It is the 33rd largest state in the United States. Pennsylvania has 51 miles (82 km) of coastline along Lake Erie and 57 miles (92 km) of shoreline along the Delaware Estuary.

The boundaries of the state are the Mason–Dixon line (39° 43' N) to the south, the Twelve-Mile Circle on the Pennsylvania-Delaware border, the Delaware River to the east, 80° 31' W to the west and the 42° N to the north, with the exception of a short segment on the western end, where a triangle extends north to Lake Erie.

Pennsylvania borders six other states: New York to the north; New Jersey to the east; Delaware to the southeast; Maryland to the south; West Virginia to the southwest, and Ohio to the west. Pennsylvania also shares a water border with the Canadian province of Ontario to the northwest across Lake Erie. Of the original Thirteen Colonies, Pennsylvania is the only state that does not border the Atlantic Ocean.

It has the cities of Philadelphia, Reading, Lebanon and Lancaster in the southeast, Pittsburgh in the southwest, the tri-cities of Allentown, Bethlehem, and Easton in the central east (known as the Lehigh Valley), the tri-cities of Scranton, Wilkes-Barre, and Hazleton in the northeast, and Erie in the northwest. Williamsport serves as the commonwealth's north-central region, with York and the state capital Harrisburg on the Susquehanna River in the central region of the commonwealth.

The state has 5 regions, namely the Allegheny Plateau, Ridge and Valley, Atlantic Coastal Plain, Piedmont, and the Erie Plain.

Pennsylvania's diverse topography also produces a variety of climates, though the entire state experiences cold winters and humid summers. Straddling two major zones, the majority of the state, with the exception of the southeastern corner, has a humid continental climate (Köppen climate classification Dfa). Greater Philadelphia has some characteristics of the humid subtropical climate (Köppen Cfa) that covers much of Delaware and Maryland to the south.

Moving toward the mountainous interior of the state, the winter climate becomes markedly colder, the number of cloudy days increases, and snowfall amounts are greater. Western areas of the state, particularly locations near Lake Erie, can receive over 100 inches (250 cm) of snowfall annually, and the entire state receives plentiful precipitation throughout the year. The state may be subject to severe weather from spring through summer into fall. Tornadoes occur annually in the state, sometimes in large numbers, such as 30 recorded tornadoes in 2011.