There are 5 US Post Offices in Nassau County serving a total of 73,213 residents equating to 14,643 residents per post office. It's estimated that approximately 116,856 packages are handled across the 5 county post offices annually. Nassau County is a county located in the state of Florida. As of the 2010 census, the population was 73,314. The county seat and largest incorporated city is Fernandina Beach. Nassau County is included in the Jacksonville Metropolitan Statistical Area. Tourism, primarily associated with Amelia Island and the many golf courses in the area, is the chief economic industry."