There are 9 US Post Offices in Sullivan County serving a total of 6,035 residents equating to 671 residents per post office. It's estimated that approximately 9,633 packages are handled across the 9 county post offices annually. Sullivan County is a county located in the U.S. state of Pennsylvania. As of the 2010 census, the population was 6,428, making it the second-least populous county in Pennsylvania. Its county seat is Laporte. The county was created on March 15, 1847, from part of Lycoming County and named for Charles C. Sullivan, leader of the Pennsylvania Senate at that time."