Beaver is a borough in 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, approximately 30 miles northwest of Pittsburgh. As of the 2010 census, the borough population was 4,531. The borough is a Tree City USA community.Robert Linn was the mayor of Beaver for 58 years, 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.