There are 4 US Post Offices in Ottawa County serving a total of 5,797 residents equating to 1,449 residents per post office. It's estimated that approximately 9,253 packages are handled across the 4 county post offices annually. Ottawa County (standard abbreviation: OT) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 6,091. The largest city and county seat is Minneapolis."