Marion is a city located in Williamson County Illinois. It is also the county seat of Williamson County. With a 2020 population of 17,356, it is the 147th largest city in Illinois and the 2089th largest city in the United States . Marion is currently declining at a rate of -0.47% annually but its population has increased by 0.95% since the most recent census, which recorded a population of 17,193 in 2010. Marion reached it's highest population of 17,757 in 2013. Spanning over 17 miles, Marion has a population density of 1,051 people per square mile.
The average household income in Marion is $62,472 with a poverty rate of 18.53%. The median rental costs in recent years comes to $740 per month, and the median house value is $115,500. The median age in Marion is 39.3 years, 36.2 years for males, and 41.9 years for females.