Chillicothe is a city in the state of Missouri and the county seat of Livingston County, Missouri, United States. The population was 9,107 at the 2020 census. The name "Chillicothe" is Shawnee for "big town", and was named after their principal town Chillicothe, located since 1774 about a mile from the present-day city of Chillicothe, Ohio.