Reflectivity images of the lower crust and uppermost mantle beneath the Illinois basin have been derived from reprocessing of several hundred kilometers of industry seismic reflection data using extended vibroseis recorrelation. The recorrelation was based on extending an originally 4-s correlated record, acquired with a 16-s sweep from 14 to 126 Hz, to the absolute limit of the full 20 s (~70 km) listening travel time. The reconstructed bandwidth includes frequency components suitable for imaging structures from signals received from both sedimentary basin reflectors and those received from reflectors in the deep crust and upper mantle. Mantle and sub-Moho reflectors are imaged down to 18 s two-way travel time (~62 km) and are observed on intersecting profiles generally dipping to the southwest and striking northwest-southeast. Occasional Moho reflections are also observed across the profiles (~12 s or ~38 km) while reflectivity in the lower crust is generally marked by intermittent horizontal packages and short, gently dipping reflections and diffraction segments. The presence of newly observed mantle reflectivity beneath the Illinois basin indicates significant upper mantle heterogeneity, relative to other parts of the USA studied using reflection methods. The relatively isolated occurrence of mantle reflections beneath the basin makes it difficult to uniquely infer their origin. However, available geologic and geophysical constraints, especially from geochemical and geochronological studies of drilled basement rocks, effectively limit the possibilities to: (1) remnants or "scars" of sub-crustal processes associated with lithospheric extension or delamination related to the melting of the Proterozoic crust that led to the emplacement of the granite--rhyolite province that underlies much of USA Midcontinent; or (2) deformation caused by plate subduction associated with the hypothetical accretion of a juvenile arc to the pre-1.6 Ga southern margin of the Laurentian continent.