Vandalia is a city located in Fayette County Illinois. It is also the county seat of Fayette County. With a 2020 population of 6,660, it is the 285th largest city in Illinois and the 4064th largest city in the United States . Vandalia is currently declining at a rate of -0.18% annually and its population has decreased by -5.42% since the most recent census, which recorded a population of 7,042 in 2010. Vandalia reached it's highest population of 7,239 in 2011. Spanning over 8 miles, Vandalia has a population density of 818 people per square mile.
The average household income in Vandalia is $51,007 with a poverty rate of 21.47%. The median rental costs in recent years comes to $625 per month, and the median house value is $83,700. The median age in Vandalia is 38.3 years, 37 years for males, and 40.9 years for females.