There are 10 US Post Offices in Antrim County serving a total of 22,943 residents equating to 2,294 residents per post office. It's estimated that approximately 36,620 packages are handled across the 10 county post offices annually. Antrim County is a county located in the U.S. state of Michigan. As of the 2010 census, the population was 23,580. The county seat is Bellaire. The name is taken from County Antrim in Northern Ireland. YMCA Camp Hayo-Went-Ha, the oldest American summer camp that sits on its original site, occupies about one square mile on the shore of Torch Lake in Central Lake Township. Boys first attended Hayo-Went-Ha (variant of Hiawatha) in 1904."