There are 7 US Post Offices in Kendall County serving a total of 102,515 residents equating to 14,645 residents per post office. It's estimated that approximately 163,625 packages are handled across the 7 county post offices annually. Kendall County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 114,736. Its county seat is Yorkville, and its most populous municipality is Oswego. Kendall County is included in the Chicago-Naperville-Elgin, IL-IN-WI Metropolitan Statistical Area. It was the fastest-growing county in the United States between the years 2000 and 2010."