Interstate 90 (I-90) in the US state of Illinois runs roughly northwest-to-southeast through the northern part of the state. From the Wisconsin state line at South Beloit, it heads south to Rockford before heading east-southeast to the Indiana state line at Chicago. I-90 traverses 124 miles (200 km) through a variety of settings, from farmland west of the Fox River Valley through the medium-density suburbs west of O'Hare International Airport, through Downtown Chicago, and through the heart of the industrial southeast side of Chicago before entering Indiana.

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.