There are 7 US Post Offices in Carroll County serving a total of 9,531 residents equating to 1,362 residents per post office. It's estimated that approximately 15,213 packages are handled across the 7 county post offices annually. Carroll County is a county located in the U.S. state of Missouri. As of the 2010 census, the county had a population of 9,295. Its county seat is Carrollton. The county was organized on January 2, 1833 from part of Ray County, Missouri and named for Charles Carroll of Carrollton, a signer of the Declaration of Independence.