There are 15 US Post Offices in Woodbury County serving a total of 18,942 residents equating to 1,263 residents per post office. It's estimated that approximately 30,234 packages are handled across the 15 county post offices annually. Woodbury County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 102,172. The county seat is Sioux City. Woodbury County is included in the Sioux City, IA-NE-SD Metropolitan Statistical Area."