There are 25 US Post Offices in Clarion County serving a total of 40,092 residents equating to 1,604 residents per post office. It's estimated that approximately 63,991 packages are handled across the 25 county post offices annually. Clarion County is a county located in the U.S. state of Pennsylvania. As of the 2010 United States Census, the population was 39,988. Its county seat is Clarion. The county was formed on March 11, 1839, from parts of Venango and Armstrong counties. Clarion County is entirely defined as part of the Pittsburgh media market."