There are 9 US Post Offices in Marshall County serving a total of 8,496 residents equating to 944 residents per post office. It's estimated that approximately 13,561 packages are handled across the 9 county post offices annually. Marshall County is a county located in the U.S. state of Minnesota. As of the 2010 census, the population was 9,439. Its county seat is Warren. Marshall County was the location of a claimed UFO incident in 1979, the Val Johnson incident."