There are 2 US Post Offices in Columbia County serving a total of 25,798 residents equating to 12,899 residents per post office. It's estimated that approximately 41,176 packages are handled across the 2 county post offices annually. Columbia County county located in the U.S. state of Florida. As of the 2010 census, the population was 67,531. Its county seat is Lake City. Columbia County comprises the Lake City, FL Micropolitan Statistical Area, which is included in the Gainesville-Lake City, FL Combined Statistical Area."