High Quality Content by WIKIPEDIA articles! The Sycamore Historic District is a meandering area encompassing 99 acres (400,000 m2) of the land in and around the downtown of the DeKalb County, Illinois, county seat, Sycamore. The area includes historic buildings and a number of historical and Victorian homes. Some significant structures are among those located within the Historic District including the DeKalb County Courthouse and the Sycamore Public Library. The district has been listed on the National Register of Historic Places since May 2, 1978.