The Flint Hills Tallgrass Prairie Preserve (FHTPP) comprises 3 parcels of land owned and protected by The Nature Conservancy of Kansas. It sits approximately 8 km (5 miles) east of Cassoday, Kansas in Butler and Greenwood counties. The preserve totals 885 hectares (2,188 acres), and this study was performed on a portion of the preserve that is 130 hectares (321 acres) in size. The FHTPP has not been grazed since its acquisition, providing a unique opportunity for comparison to similar preserves. Though the flora of Butler County is relatively well documented, no floristic checklist has been published for the county or a site within. The goals of this study were to document all vascular plant species present on the site, compare the floristic composition of the FHTPP to that of two comparable properties, and assess potential vegetation differences between previously tilled and untilled portions of the FHTPP. Over three seasons 542 collections were made from which 274 taxa (176 genera and 59 families) were identified. Native taxa comprised 89% of observed taxa. Of the 29 non-native taxa, one taxon (Lespedeza cuneata) is classified as a category C noxious weed in Kansas. Seven species are county records. Comparisons with unpublished checklists from the nearby Youngmeyer Ranch and Tallgrass Prairie National Preserve establish that the FHTPP contains comparable levels of overall species conservatism, although riparian and woodland areas at the FHTPP host fewer conservative taxa. This suggests that the lack of recent grazing history at the FHTPP has not notably increased or decreased basic levels of floristic quality relative to similar sites with grazing. Although measures of taxonomic richness and floristic quality did not differ between tilled and untilled plots, the relative abundance of native taxa was significantly higher on plots that were untilled. Seven native taxa were significantly correlated with untilled plots, while two exotic taxa and three native taxa were significantly associated with previously tilled plots. This suggests that a comparable plant community has re-established following tillage at the FHTPP, although these areas might be more vulnerable to invasion by non-native species.