There are 16 US Post Offices in Mchenry County serving a total of 268,046 residents equating to 16,753 residents per post office. It's estimated that approximately 427,831 packages are handled across the 16 county post offices annually. McHenry County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 308,760, making it the sixth-most populous county in Illinois. Its county seat is Woodstock. McHenry County is one of the five collar counties of the Chicago-Naperville-Elgin, IL-IN-WI Metropolitan Statistical Area. Long known as a center of agriculture and recreation, it has more recently experienced rapid rates of suburbanization and urbanization, but remains primarily agricultural and rural."