sycamore,_illinois | region | dekalb_county,_illinois <sep> 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 17,519 at the 2010 census sycamore is the county seat of dekalb county and was named after the sycamore tree 
sycamore is located in dekalb county. illinois.sycamore is the county seat of dekalb county illinois