There are 5 US Post Offices in Alexander County serving a total of 8,093 residents equating to 1,619 residents per post office. It's estimated that approximately 12,917 packages are handled across the 5 county post offices annually. Alexander County is the southernmost county of the U.S. state of Illinois. As of the 2010 census, the population was 8,238. Its county seat is Cairo. Alexander County is part of the Cape Girardeau, MO-IL Metropolitan Statistical Area."