Collection records from 1833-1976 for 301 aliens for Hancock and McDonough counties Illinois [USA] indicate 1/3 (75% cultivated)-including 6 sole Illinois records-should be excluded because of no collections for 24-130 yr. Of the remaining 204: over 26% have been reported since 1952; 79% are naturalized and the rest casuals; 83% are from the Old World, 11% from other states and 5% from the New World tropics; 55% have been cultivated; over 90% occur throughout most of Illinois; 84% are weeds in the USA; 91% grow in disturbed mesic habitats and only 2 are aquatic. Of the 1121 spp. recorded in the study area (820 natives and 301 alines), 130 natives are extinct and 97 aliens excluded. Today aliens comprise 23% of the present flora compared to 6% in 1846. The flora is in a dynamic state of flux due to continued disturbances causing the extinction of native species (16% by 1976), and a parallel increase in the number, status and distribution of alien species.