DeKalb County Courthouse (Illinois)

The Sycamore Public Library, in Sycamore, Illinois, was erected in 1905 in the former location of Mansion House, Sycamore's oldest structure. Construction began in May of that year and the library officially opened to the public on Thanksgiving Day, 1905. The library joined the National Register of Historic Places in May 1978 with the rest of the Sycamore Historic District. The library still operates, as of 2019, as the Sycamore library. The library was erected with the help of a $10,000 grant from Andrew Carnegie in 1905.

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. There are over 200 properties within the irregular boundaries of the Sycamore Historic District. Of those, 187 are considered contributing properties to the historic district, and 22 are non-contributing. Of all of the district's homes and buildings 75% fit within the historic district concept. Some of the major structures include several prominent Queen Anne style mansions, the Sycamore library, the DeKalb County Courthouse, and dozens of mid- to late 19th-century houses.

The Charles O. Boynton Carriage House is a prominent structure in the Sycamore Historic District, located in Sycamore, Illinois. The Sycamore Historic District was added to the National Register of Historic Places in 1978. The Carriage House is considered one of more than 150 contributing properties to the overall historic integrity of the district.

The Carlos Lattin House was built by Sycamore, Illinois' first permanent settler, Carlos Lattin. It lies within the boundaries of the Sycamore Historic District and is listed as one of the contributing structures in the district. The Sycamore Historic District was added to the National Register of Historic Places in 1978.

The George's Block, once known as the James Block, is a 19th-century structure located in Sycamore, Illinois, along Illinois Route 64 (State Street) as it passes through the DeKalb County seat. The Block is part of the Sycamore Historic District and as such is listed on the National Register of Historic Places. The district joined the Register in May 1978. The building dates from 1857 when it was owned by Daniel P. James but by the 1860s the building has become known as George's Block.

The Peter Johnsen Rooming House is an historic building near downtown Sycamore, Illinois. The red brick structure stands in the 100 block of South Main Street and is considered a contributing structure to the overall historic integrity of the Sycamore Historic District. The district was added to the National Register of Historic Places in May 1978.

The William W. Marsh House in Sycamore, Illinois, the county seat of DeKalb County, has been listed on the National Register of Historic Places since 1978. The 1873 house was home to William W. Marsh, an inventor and is located along Illinois Route 64 as it passes through Sycamore. The Marsh House was built in the Italianate style and contains distinctive Italianate elements such as a cupola, a low pitched roof and eaves supported by corbels.

The D. B. James House is located in Sycamore, Illinois and is part of the Sycamore Historic District. The district was entered on the National Register of Historic Places in 1978. The James House is one of 226 properties located within the district boundaries. It stands on the corner of Exchange and Main Streets behind the DeKalb County Courthouse.

The Row Houses in Sycamore, Illinois are a small collection of historic terraced homes near the city's downtown. The building is considered by the National Register of Historic Places to be a contributing structure to the overall historic nature of the Sycamore Historic District. The district was added to the Register in May 1978. The buildings stand on the corner of Elm and California Streets in Sycamore.

The Frederick B. Townsend House is located in the DeKalb County, Illinois county seat of Sycamore. The home is within the boundaries of the Sycamore Historic District. The district was designated and listed on the National Register of Historic Places in May 1978. The Queen Anne style home was designed and constructed in 1890 or 1892 by the same architect and general contractor responsible for Altgeld Hall at Northern Illinois University and the nearby DeKalb County Courthouse, as well as the courthouse in Lee County.

The Elmwood Cemetery Gates mark the east and north entrances to the Elmwood Cemetery in Sycamore, Illinois. The cast iron gates were likely built in 1865, the year the cemetery opened and the one emblazoned on the gates, though records of their construction have been lost. While cast iron was commonly used for building facades at the time, the gates are a rare example of its use in landscape architecture. The gates have a Serlian design with a wide central road entry and narrower pedestrian gates on either side; square columns separate the gates. An arch bearing the cemetery's name rises above the center entrance, while lintels span the side entrances; both the arch and the lintels feature ornamental designs. The Illinois Historic Structures Survey described the gates as the best extant example of iron cemetery gate design in the state.A number of prominent past citizens of both Sycamore and nearby DeKalb are buried in the cemetery. The gates have been listed on the National Register of Historic Places since November 28, 1978.

The U.S. Post Office in Sycamore, Illinois is listed on the National Register of Historic Places as part of the Sycamore Historic District. The district was designated and listed in May 1978. It stands directly across the street from another key structure in the district, the Sycamore Public Library and cross-corner from the district's largest structure, the DeKalb County Courthouse. It is open M-F from 8:30 am – 6:00 pm, Sat. from 9:00 am – 3:00 pm, and it is closed on Sunday.