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.

Sycamore is a city in DeKalb County, Illinois, United States. It has a commercial district based and centered on Illinois Route 64. The population was 18,577 at the 2020 census, up from 17,419 at the 2010 census. Sycamore is the county seat of DeKalb County and was named after the sycamore tree.