There are 5 US Post Offices in Menard County serving a total of 12,757 residents equating to 2,551 residents per post office. It's estimated that approximately 20,362 packages are handled across the 5 county post offices annually. Menard County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 12,705. Its county seat is Petersburg, which is also the location of the only stop light in the county. Menard County is part of the Springfield, Illinois, IL Metropolitan Statistical Area."