Mercer is a borough in Mercer County, Pennsylvania, United States. The population was 2,391 at the 2000 census. It is the county seat of Mercer County. Mercer is part of the Youngstown–Warren–Boardman, OH-PA Metropolitan Statistical Area.
The community was named after physician Brigadier General Hugh Mercer. Brigadier General Mercer was a close friend to General Washington and became a rallying point for the Battle of Princeton.
Mercer is the birthplace of the 19th century painter Samuel Waugh, actor and impresario J C Williamson born here in 1845 (full name James Cassius Williamson) as well as musician Trent Reznor, creator of the band Nine Inch Nails. Mercer is also known for its Memorial Day Parade with the main street lined with 500 flags. Each February it holds Penn's Woods West Arts & Crafts Festival at the Mercer Area High School as well Victorian Days in the summer. Many attend the outdoor concerts by the Mercer Community Band on Friday evenings each summer. Facebook has links back to this small town, including that of the Winklevoss twins' father attended Mercer High School.