The dynamics of soil organic carbon (SOC) are affected by many factors including land use, management history, soil type, climate, and soil landscape processes. The primary objective of this research was to compare the storage of SOC on sloping woodland and cropland landscapes of northwestern Illinois. The cropland area was cultivated using a moldboard plow system for 125 years and then the primary tillage was changed to chisel plow for the last 25 years. The woodland area was never cleared or cultivated. The SOC concentrations of various soil layers, to a depth of 0.5 m, were measured. The woodland landscape had significantly higher SOC in the surface layers on all landscape segments than at the cultivated site. For both land uses, the subsurface layers had similar SOC levels. Results suggested that the cropland landscape retained 51.9 per cent of the total SOC on a volumetric basis during the last 150 years of cultivation, soil erosion and agricultural use. The other 48.1% of the SOC was either deposited in the water or released to atmosphere. Results suggest that if northwestern Illinois soils are used for cropland, additional SOC will be released to stream or atmosphere and not maintained in soil even with a chisel plow system.