There are 4 US Post Offices in Lamar County serving a total of 69,184 residents equating to 17,296 residents per post office. It's estimated that approximately 110,425 packages are handled across the 4 county post offices annually. Lamar County is a county located in the U.S. state of Mississippi. As of the 2010 census, the population was 55,658. Its county seat is Purvis. Named for the post-Civil War Mississippi statesman Lucius Quintus Cincinnatus Lamar, the county was carved out of Marion County to the west in 1904. Lamar County is part of the Hattiesburg, MS Metropolitan Statistical Area. It is largely a rural county, except for its northeast quarter."