There are 7 US Post Offices in Delaware County serving a total of 13,500 residents equating to 1,929 residents per post office. It's estimated that approximately 21,548 packages are handled across the 7 county post offices annually. Delaware County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 17,764. The county seat is Manchester. The county was named in honor of Delaware."