Round Lake Beach is a northern suburb of Chicago in Lake County, Illinois, United States. Per the 2020 census, the population was 27,252. The United States Census Bureau defines an urban area of northwest Chicago-area suburbs that are separated from Chicago's urban area, with Round Lake Beach as the principal city: the Round Lake Beach–McHenry–Grayslake, IL–WI urban area had a population of 261,835 as of the 2020 census, making it the 155th largest in the United States.