Biological diversity is studied at many geographical scales, but specimen collecting is invariably done at a local level. Collecting of animal and plant specimens leads to the compilation of checklists for multiple small areas, which are sometimes merged to produce larger, regional checklists. Such an approach was employed to study the regional vascular flora of 22 national parks of the midwestern United States. Total number of plant taxa (species level and below) ranged from 86 at Hopewell Culture National Historical Park to 1,399 at Indiana Dunes National Lakeshore and averaged 520 per park. Infraspecific taxa were 12% or less of all taxa at all parks and averaged 7%. Genera per parkranged from 70 to 562, and families ranged from 41 to 145. Non-native species averaged 95 per park, or about 27% on average of the total number of taxa per park. The aggregated regional flora contained just over 2,900 taxa, 828 genera and 160 families. Eleven percent of the taxa were below the species level. Almost 17% of the taxa were non-native, a relatively large percentage, but not out of the range of percentages reported in the literature. The observed and estimated numbers of taxa for this region were in good agreement with other estimates for these latitudes and for a standard regional size. However, the parks do not represent their respective state floras very well when they are aggregated at that scale. Indiana was the best represented state with 65% of the state flora found in the parks, while only 25% of each state's flora were represented by parks in Iowa, Kansas, and Nebraska, and the average representation was only 42%.