|Location||200 yards (180 m) east of the Eldred-Hillview road, 5.5 miles (8.9 km) south of Eldred|
|Nearest city||Eldred, Illinois|
|Area||25 acres (10 ha)|
|NRHP Reference #||72000460|
|Added to NRHP||June 19, 1972|
The Koster Site is a prehistoric archaeological site located south of Eldred, Illinois. The site includes eleven settlements dating from 5100 B.C. to 1000 A.D. Nine of the settlements were occupied during the Archaic period, while the other two were inhabited during the Woodland period. The soil strata containing the settlement remains are separated by additional layers of soil, making the site exceptionally well-preserved.
The site includes one of the oldest known cemetery sites in eastern North America. The cemetery site has provided researchers with evidence that Early Archaic civilizations had specific burial practices and buried their dead in cemeteries. Other significant discoveries made at the site include early evidence of North Americans using stones to grind food and keeping domesticated dogs. The discovery of permanent residences and items which could not be easily transported at the site suggests that it was a large permanent village; at the time of its discovery. Excavations at the site have also yielded a variety of stone tools, which were used for various purposes and also indicate long-term habitation of the site.
Before excavations began at the site, Theodore and Mary Koster used the property as a farm. Archaeologists from the Center for American Archeology and Northwestern University first investigated the property in 1969; their work at the site continued through the late 1970s. The excavation became one of the largest of its era and drew over 10,000 yearly visitors; it is considered to be the Center for American Archeology's most important discovery. The site was added to the National Register of Historic Places on June 19, 1972.
- "National Register Information System". National Register of Historic Places. National Park Service. 2010-07-09.
- Struever, Stuart. National Register of Historic Places Inventory - Nomination Form: The Koster Site. National Park Service, 1971-11-04.
- "Archaic Archaeological Sites". Illinois State Museum. Retrieved November 16, 2013.
- Borman, Maggie (October 10, 2009). "Window into the past: Koster site remains unique 40 years later". The Telegraph. Retrieved November 16, 2013.