Woodstock is a city in and the county seat of 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.