Barrens were areas of scrub oak and prairie plants that were noted by Government Land Office (GLO) Surveys in Illinois. Surveyors described four vegetation types: prairie, barrens, scattering timber, and forest. Since settlement, these vegetation types have nearly disappeared. We used GIS and the GLO survey notes for Jersey and Greene Counties in southwestern Illinois to locate and estimate the area of barrens present at the time of the surveys. Using these estimates it was possible to determine that barrens covered about ten percent of each county. The larger barrens areas were surrounded by prairie and located in the more level eastern portions of the counties. Carya spp., Quercus marilandica, and Q. stellata were more abundant in barrens than in other vegetation types. Surveyor-designated prairies were located both on prairie soils (argiudolls) and forest soils (hapludalfs). Barrens, scattering timber, and forest were all found on forest soils and on steeper slopes than prairies. The distribution of vegetation types suggests that barrens represent an expansion of woody vegetation onto especially vulnerable prairie sites during the Little Ice Age (1450 to 1850 AD).