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.

The DeKalb County Courthouse is located in the county seat of DeKalb County, Illinois, U.S., the city of Sycamore. The Classical Revival structure sits on a square facing Illinois Route 64 as it passes through the city. The current courthouse was constructed in 1905 amid controversy over where the courthouse and thus, ultimately, the county seat would be located. The current building is the third structure to bear the name "DeKalb County Courthouse." DeKalb County's Courthouse still serves as the county's primary judicial center and is a contributing property to the Sycamore Historic District. The district joined the National Register of Historic Places in 1978. As the county's primary courthouse for over 100 years, the site has been host to many trials, including prominent murder cases.