There are 9 US Post Offices in Mahaska County serving a total of 20,951 residents equating to 2,328 residents per post office. It's estimated that approximately 33,440 packages are handled across the 9 county post offices annually. Mahaska County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 22,335. The county seat is Oskaloosa. Mahaska County comprises the Oskaloosa, IA Micropolitan Statistical Area."