Beaver is a borough in and the county seat of Beaver County, Pennsylvania, United States, at the confluence of the Beaver and Ohio Rivers. As of the 2000 census, the borough population was 4,775, having dropped from 5,641 in 1940.
Robert Linn was the mayor of Beaver for 58 years (1946–2004), making him the longest serving mayor in the United States. The borough was the home of influential U. S. Senator "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.