There are 12 US Post Offices in Winnebago County serving a total of 167,718 residents equating to 13,977 residents per post office. It's estimated that approximately 267,697 packages are handled across the 12 county post offices annually. Winnebago County is a county in the U.S. state of Wisconsin. As of the 2010 census, the population was 166,994. Its county seat is Oshkosh. Winnebago County comprises the Oshkosh-Neenah, WI Metropolitan Statistical Area, which is included in the Appleton-Oshkosh-Neenah, WI Combined Statistical Area."