Centralia is a city in Boone County in the U.S. state of Missouri. The population was 4,541 at the 2020 census, with an estimated population of 4,244 in 2018. A very small portion of the city lies in Audrain County. The Boone County portion of Centralia is part of the Columbia Metropolitan Statistical Area, while a small part in Audrain County is part of the Mexico Micropolitan Statistical Area.