The 590 ha Sand Prairie-Scrub Oak Nature Preserve in Mason County, Illinois contains remnant dry sand prairies, sand savanna, sand forest, and successional fields. Purchased in 1969, the abandoned agricultural fields have been allowed to re-vegetate naturally. The vegetation of a mature dry sand prairie was compared with two successional fields, one 60- and one 30-years-old. The mature dry sand prairie was dominated by Schizachyrium scoparium (little bluestem), Dichanthelium villosissimum (hairy panic grass), Tephrosia virginiana (goat's-rue), Ambrosia psilostachya (western ragweed), and Opuntia humifusa (common pricklypear). Eragrostis trichodes (sand love grass) dominated the 60-year-old successional fields. The 30-year-old successional field was dominated by Eragrostis trichodes, Strophostyles helvula (wild bean), and Monarda punctata (horsemint). A total of 393 vascular plant species were documented for the preserve.