Centralia is a town located in Marion, Washington, Clinton, and Jefferson Counties in the U.S. state of Illinois. The population was 13,032 at the 2010 census. The town was founded because it was the point where the two original branches of the Illinois Central Railroad, built in 1853, converged. The town is named for the railroad. The current mayor is Tom Ashby.
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.
Centralia is located approximately 60 miles (100 km) east of St. Louis, Missouri. It is on the border of south-west Marion County with portions of the city located in Clinton, Washington and Jefferson counties, and is 10 miles (16 km) north of exit 61 of I-64 and 10 miles (16 km) west of exit 109 of I-57. Centralia is one of three Illinois cities with portions in four counties, the others being Barrington Hills and Aurora.