Crystal Lake is a city in McHenry County in the U.S. state of Illinois. Named after a lake 1.6 miles (2.6 km) southwest of the city's downtown, Crystal Lake is 45 miles northwest of Chicago. The population was estimated at 39,829 in July 2019, a 2.3% decrease from 2010. Crystal Lake is the largest city in McHenry County, part of the Chicago metropolitan area.
The City of Crystal Lake traces its origin to two separate communities which were established in the 1800s. Those communities were generally known as Nunda and Crystal Lake. In 1835, Ziba S. Beardsley had come to the shores of the lake and commented that the "waters were as clear as crystal", thereby giving the lake its name. Ziba Beardsley continued south to Naperville. In February 1836, the first white settlers, Beman and Polly Crandall and six of their ten children, came from New York State traveling to Crystal Lake in a covered wagon. Their original cabin was built in the vicinity of today's intersection of Virginia Street and Van Buren Street. Four of the Crandall children were born there.