The McHenry County Courthouse is located at 2200 North Seminary Avenue, Woodstock, IL 60098; phone: 815-334-4000.
Named for Colonel William McHenry, a regimental commander during the Black Hawk War of 1832, McHenry County was created in 1836 from the northern and western portions of Cook County. The first county seat, McHenry, was located in the center of the county until Lake County was separated from McHenry several years later, leaving the town of McHenry on the new eastern border. Thus, in 1844, Alvin Judd platted a new town in the county's center called, appropriately, Centerville, in the hopes that the county seat might be moved. The plat, a central square oriented to the compass points with streets originating at the centers of the four sides, the whole, surrounded by a rectangular grid, was recorded by George Dean in June, 1844. The scheme was successful, Centerville was named the new county seat, and on September 4, 1844, the county government moved to the new, 1-story frame building constructed in the town square. The name was changed to Woodstock in February 1845 at the suggestion of an early settler, Joel Johnson, to honor his home town of Woodstock, Vermont.
The first railroad through the county, the Galena and Chicago Union Railway, was completed in 1854. The tracks ran south of Woodstock and stopped at Huntley, Union and Marengo.