There are 9 US Post Offices in Butler County serving a total of 15,215 residents equating to 1,691 residents per post office. It's estimated that approximately 24,285 packages are handled across the 9 county post offices annually. Butler County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 14,867. Its county seat is Allison. The county was organized in 1854 and named for General William O. Butler."