Round Lake Park, IL has a population of 7,989 and is the 4,684th largest city in the United States. The population density is 3,870 per sq mi which is 1641% higher than the Illinois average and 4172% higher than the national average. The median age in Round Lake Park is 40 which is approximately 7% higher than the Illinois average of 37. In Round Lake Park, 64% of the population over 15 years of age are married, 58% speak English and 39% speak Spanish. 65% of Round Lake Park residents were born in Illinois, 13% were born out of state, 1% were born outside of the United States and 22% were foreign born.