There are 12 US Post Offices in Fillmore County serving a total of 23,481 residents equating to 1,957 residents per post office. It's estimated that approximately 37,478 packages are handled across the 12 county post offices annually. Fillmore County is a county located in the U.S. state of Minnesota. As of the 2010 census, the population was 20,866. Its county seat is Preston. Fillmore County is included in the Rochester, MN Metropolitan Statistical Area."