There are 5 US Post Offices in Poweshiek County serving a total of 18,554 residents equating to 3,711 residents per post office. It's estimated that approximately 29,614 packages are handled across the 5 county post offices annually. Poweshiek County is a county located in southeastern part of the U.S. state of Iowa. As of the 2010 census, the population was 18,914. The county seat is Montezuma. The county is named for the Indian chief of the Fox tribe who signed the treaty ending the Black Hawk War. It is located along Interstate 80, between Des Moines and Iowa City."