There are 2 US Post Offices in Madison County serving a total of 12,943 residents equating to 6,472 residents per post office. It's estimated that approximately 20,658 packages are handled across the 2 county post offices annually. Madison County is a county located in the Lead Belt region of the U.S. state of Missouri. As of the 2010 census, the population was 12,226. Its county seat and largest city is Fredericktown. The county was officially organized on December 14, 1818, and was named after President James Madison. Mining has been a key industry in this area with Madison County recorded as having the oldest lead mine west of the Mississippi River.