Round Lake is a city located in Illinois. With a 2020 population of 18,098, it is the 139th largest city in Illinois and the 2011th largest city in the United States. Round Lake is currently declining at a rate of -0.49% annually and its population has decreased by -1.04% since the most recent census, which recorded a population of 18,289 in 2010. Round Lake reached it's highest population of 18,608 in 2014. Spanning over 6 miles, Round Lake has a population density of 3,256 people per square mile.
The average household income in Round Lake is $92,496 with a poverty rate of 6.33%. The median rental costs in recent years comes to $1,313 per month, and the median house value is $187,100. The median age in Round Lake is 34.5 years, 36 years for males, and 33.5 years for females. For every 100 females there are 89.7 males.