It would also be worth checking shorebird and songbird "migrant traps" in other more northerly areas of the state as well for possibly one of the largest push of migrants so far this autumn. View the current radar here.
Why is this happening? Looking from the mixed surface analysis, a cold front pushed through Illinois today, shifting winds from being southerly to west-northwesterly. This means the birds are not fighting a southerly headwind anymore while trying to migrate; in fact, they are even receiving a bit of a tailwind which probably explains why the radar is lighting up tonight.
One can see from the two wind maps below that the winds are indeed from the west-northwest and at quite a moderate clip, 10 to 15 mph.
Birds that one can expect to find can be seen at Birdcast's regional migration forecasts, found here. Another helpful tool is eBird.org's species occurrence chart for Illinois which shows all species that have been documented in Illinois and when exactly one could expect to find them in their greatest abundance from past observations.
In the SHOREBIRD department, one can expect to find continuing species that have been reported recently as well as continuing and possibly even slightly larger influxes of late species like Black-bellied and A. Golden Plovers, Ruddy Turnstone, Sanderling, Baird's, Buff-breasted, and Semipalmated Sandpipers, and Wilson's Snipe & Phalarope. For both plovers and Buff-breasted Sandpipers, head to the sod farms in rural areas and for all other species it would be worth checking Lake Michigan shoreline and inland shorebird hotspots like Emiquon and Goofy Ridge. One tip is to check these areas in the morning before the heat mirages/waves get in the way of viewing these typically far-away birds.
Regarding PASSERINES, Alder & Least Flycatchers, Swainson's Thrush, and warblers like Golden-winged, Black-and-White, Tennessee, Nashville, Mourning, Cape May, N. Parula, Magnolia, Bay-breasted, Blackburnian, Chestnut-sided, Blackpoll, Black-throated Green, Canada, and Wilson's should all be making noteworthy appearances in their respective "migrant traps" within the next few days, if not already.