Round Lake Park, IL has a population of n/a and is the n/a largest city in the United States. The population density is n/a per sq mi which is equal to the Illinois average and equal to the national average. The median age in Round Lake Park is n/a which is approximately equal to the Illinois average of n/a. In Round Lake Park, n/a of the population over 15 years of age are married, n/a speak English and n/a speak Spanish. n/a of Round Lake Park residents were born in Illinois, n/a were born out of state, n/a were born outside of the United States and n/a were foreign born.