Beaver is a borough and the county seat of Beaver County in the U.S. state of Pennsylvania. It is located at the confluence of the Beaver and Ohio Rivers. As of the 2010 census, the borough population was 4,531. The town is a Tree City USA community.
Robert Linn was the mayor of Beaver for 58 years (1946–2004), making him one of the longest serving mayors in the United States. The borough was the home of influential U. S. Senator Matthew "Boss" Quay.
The area around Beaver was originally home to the Shawnee tribe. Later, the Mingo, Lenape, and other displaced groups moved into the area. The area was part of the Ohio Country that was in dispute during the French and Indian War.
Beaver became the site of Fort McIntosh, a Revolutionary War era Patriot frontier fort. After the war, the fort was the home of the First American Regiment, the oldest active unit in the US Army. The fort was abandoned in 1788 and razed a short time later. By then, the frontier had moved westward and there was no further need for a permanent garrison to protect the area.
The town was laid out in 1792. In 1800, it became the county seat of the newly formed Beaver County. The first county court was established in the town in 1804. The town's growth was steady until 1879 when the arrival of the Pittsburgh and Lake Erie Railroad caused a major growth spurt. In February 1884 a massive flood caused extensive damage. In 1974, an archeological excavation was conducted at the site of Fort McIntosh.
In late 2007, local officials proposed the consolidation of Beaver with Brighton Township. According to a report by the Governor's Center for Local Government Services, the two municipalities would possibly derive a significant financial benefit from uniting. Also being considered was the type of combination: either merger, in which one of the municipalities would be annexed by the other, or consolidation, in which the two would become a single new municipality under a new name. Any union would have required voter approval.