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is a city in DeKalb County, Illinois, United States. The population was 12,020 at the 2000 census, and as of the 2005 estimate it was 14,866. It is the county seat of DeKalb County.
Sycamore is located at (41.983850, -88.694091). The city is located along Illinois Route 64 (State Street in Sycamore) about southeast of Rockford and west-northwest of Chicago. It is along the south bank of the East Branch of the South Branch Kishwaukee River in DeKalb County.
According to the United States Census Bureau, the city has a total area of 5.5 square miles (14.2 km²), of which, 5.5 square miles (14.2 km²) of it is land and 0.04 square miles (0.1 km²) of it (0.36%) is water. The terrain in Sycamore, and the surrounding area, is gently rolling and contains rich soil which was originally heavily forested.