Oglesby (zip code 61348) is a city in LaSalle County, Illinois, United States. The population was 3,647 at the 2000 census. It is part of the Ottawa–Streator Micropolitan Statistical Area. Oglesby is located near the confluence of the Illinois River and the north-flowing Vermilion River. It was originally called "Portland", due to the cement mined and manufactured in the area that was similar to Portland Cement from England. It was renamed in honor of Richard Oglesby, a former Governor of Illinois. The surface ground layers around Oglesby has excellent exposed limestone and coal, as well as riverine transport. It soon became an important center for cement manufacture. The term "Portland cement" refers to the cement developed in England; that made in early Oglesby was almost identical. Illinois Valley Community College and Oglesby Washington Public School are located in Oglesby.