McHenry County is a county located in the U.S. state of Illinois. According to the 2020 Census, it had a population of 310,229, making it the sixth-most populous county in Illinois. Its county seat is Woodstock. McHenry County is one of the five Illinois collar counties in the Chicago-Naperville-Elgin, IL-IN-WI Metropolitan Statistical Area. Long known as a center of recreation along with agriculture in the western portion, it has more recently experienced rapid rates of suburbanization, exurbanization and urbanization, but the western portions of the county remain primarily agricultural and rural.

Woodstock is a city in McHenry County, Illinois, United States. It is located 51 miles northwest of Chicago, making it one of the city's outer-most suburbs. Per the 2020 census, the population was 25,630. The city's historic downtown district and turn-of-the-century town square is anchored by the landmark Woodstock Opera House and the Old McHenry County Courthouse. In 2007 Woodstock was named one of the nation's Dozen Distinctive Destinations by the National Trust for Historic Preservation.