Government Land Office (GLO) survey records were used to reconstruct the presettlement floodplain landscape at the confluence of the Illinois and Mississippi rivers. Presettlement prairie and forest land covers were determined by digitizing GLO plat maps using a computerized geographic information system (GIS). A case history of land cover change was determined by comparing this presettlement map to GIS land cover maps for 1903, 1935, and 1975. Data from witness trees and current forest samples were used to compare presettlement and present forest composition and structure. Results indicate that approximately 56% of the presettlement floodplain was forested, while 41% was prairie. The presettlement forests were generally open (86.8 stems/ha) and consisted of several dominant tree species. In contrast, the present forest is more dense (489 stems/ha) and is dominated by silver maple (Acer saccharinum). Early settlement had little affect on the spatial distribution of forest cover, but river impoundment in 1938 reduced forests to approximately 35% of the floodplain. Prairies were converted to agriculture during the middle 1800s and now occupy only 6% of the floodplain. Overall, the floodplain landscape and vegetation patterns present today are very different from their presettlement conditions. The major activities responsible for these changes were timber harvesting, agriculture, and river impoundment.