Crystal Lake is a city located in southeastern McHenry County in the northeastern part of the US state of Illinois. It is named after Crystal Lake, a lake located 1.6 miles (2.6 km) west-southwest of downtown Crystal Lake. Crystal Lake is about 45 miles northwest of Chicago. The population was 38,000 at the 2000 census, but as of 2010 the population is at 40,743. Crystal Lake is the largest city in McHenry County, part of the Chicago metropolitan area.