Quantifying the impact of long-term agricultural land use on soil organic C (SOC) is important to farmers and environmental policy makers, but data are critically lacking. We determined SOC and related pools under conventional-tillage cropping (5-40 years), conservation-tillage cropping (5-30 years), and pasture (10-60 years) from farms in the Southern Piedmont and Coastal Plain Major Land Resource Areas. Soil at depths of 0-5, 5-12.5, and 12.5-20 cm was collected from 72 fields in GA, SC, NC and VA and analyzed for total C, particulate organic C and microbial biomass C. The experimental design allowed us to separate the influences of land use from mean climatic conditions (i.e., temperature and precipitation) and physiographic region. Summed to a depth of 20 cm, SOC averaged 36.5 Mg C ha^-1 in the Coastal Plain and 32.2 Mg C ha^-1 in the Piedmont. Soil organic C averaged 41.9 Mg C ha^-1 under pasture, 34.0 Mg C ha^-1 under conservation tillage and 27.2 Mg C ha^-1 under conventional tillage. The greatest statistical differences in SOC among land uses occurred at the 0-5 cm depth.  These data will be used to evaluate the potential of agricultural land use to store SOC and alter soil quality under different conditions in the southeastern USA.