There are 8 US Post Offices in Grundy County serving a total of 11,363 residents equating to 1,420 residents per post office. It's estimated that approximately 18,137 packages are handled across the 8 county post offices annually. Grundy County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 12,453. The county seat is Grundy Center. The county is named for Felix Grundy, former U.S. Attorney General. Grundy County is included in the Waterloo-Cedar Falls, IA Metropolitan Statistical Area.