The Grundy County courthouse, of which the north-facing section was built in 1912-1913, is a Classical Revival structure with a façade of cut limestone. The structure is one of several Illinois courthouses designed by architect Joseph W. Royer.[3]
The historic circuit courtroom continues to occupy and use second floor space in the original building. In 2009, the Illinois State Bar Association (ISBA) celebrated the 1912 judicial courtroom.[4]
In 1975-1976, the county built a major annex structure south of the original building. The annex contains law enforcement space, with limited fenestration (windows) signaling to passers-by the presence of the county jail.[3]
Two earlier Grundy County courthouses have disappeared. The first courthouse was a frame structure used in 1842-1858, and the second courthouse was used in 1858-1912.[3]