Vandalia is a city in Fayette County, Illinois, 69 miles (111 km) northeast of St. Louis, on the Kaskaskia River. In 1900, 2,665 people lived in Vandalia; in 1910, 2,974; and in 1940, 5,288. The population was 6,975 at the 2000 Census. It is the county seat of Fayette County, the home of the Vandalia State House State Historic Site (1836), and was a terminus of the National Road. In 1819, it was decided to move the state capital from Kaskaskia to Vandalia. Since 1839, Springfield has been the capital.