Centralia is a city located in Marion, Washington, Clinton, and Jefferson Counties in the U.S. state of Illinois. The population was 14,136 at the 2000 census. The town was founded because it was the point where the two original branches of the Illinois Central Railroad, built in 1856, converged. The town is named for the railroad. The current mayor is Rebecca Ault. Because of its unique location within multiple counties, portions of Centralia are associated with different Core Based Statistical Areas (CBSAs). The Centralia Micropolitan Statistical Area includes all of Marion County. The Clinton County portion of the city is considered part of the St. Louis, MO–IL Metropolitan Statistical Area, while the Jefferson County portion lies within the Mt. Vernon Micropolitan Statistical Area. The portion of Centralia in Washington County is not considered part of any metropolitan or micropolitan area.