Vandalia is a city in Fayette County, Illinois, United States, 69 miles (111 km) northeast of St. Louis, on the Kaskaskia River. From 1819 to 1839 it served as the state capital of Illinois. Vandalia was the western terminus of the National Road. Today it is the county seat of Fayette County and the home of the Vandalia State House State Historic Site (1836). The population was 6,975 at the 2000 census.
The history of the name Vandalia is uncertain. Different theories can be found in almost all of the books written about Vandalia over the years.
In her book Vandalia: Wilderness Capital of Lincoln's Land, Mary Burtschi tells of a conversation between one of the original surveyors of the town and a Vandalia resident. The surveyor, Colonel Greenup, explained that Van was suggested by one of the men. He recommended this as an abbreviation to the word vanguard meaning the forefront of an advancing movement. Another suggestion was made for the term dalia, derived from the Anglo-Saxon word dale which means a valley between hills. Greenup takes credit in the conversation for connecting the two terms to form the name Vandalia. This theory does hold water since Greenup was one of the surveyors and the terms describe the capital city.