Climate change and landscape alterations may influence biodiversity by shifting species distributions or causing local extirpations. Museum records are needed in order to track these changes over long periods of time. Bees are a group of organisms known to be in global decline, but tracking regional shifts is difficult. In Illinois, where there have been significant alterations to the landscape, no bee species checklist is available to compare recent collecting efforts. We used museum specimens from Illinois housed at the Illinois Natural History Survey (INHS) at the University of Illinois at Urbana-Champaign, augmented by specimen records from other museums, to investigate the use of museum collections to identify species occurrences and possible declines. The result is a preliminary state checklist of 491 species of bee, with an additional 51 records considered either doubtful or possible but needing confirmation. We report 74 confirmed new state records compared to records housed at INHS, with five additional species considered doubtful and four possible but needing confirmation. Three putatively undescribed species include two Andrena species and one Lasioglossum (Dialictus) species, although further verification is needed to resolve their status. Continued support for natural history collections and the institutions that maintain them is essential for further research on the impacts to ecosystems caused by human and natural influences and to identify areas and species in need of conservation.