There is a heavy focus on the Greater St. Louis area, as that is where the majority of my research has occurred, though I have included information on resources that are pertinent to other areas in the state
American Bottom RiverWeb
The RiverWeb:American Bottom Landing Site contains a large digital archive of artifacts related to the American Bottom region, defined as the area south of the confluence of the Missouri, Mississippi and Illinois rivers. This includes portions of St. Clair, Randolph, Madison, and Monroe Counties in Illinois. Most of the information on the site appears to be centered on the Cahokia Mounds, and East St. Louis.
Illinois Online Archives
Online databases provided by the Illinois office of the Secretary of State. Includes a database of Illinois Veterans, a statewide marriage index from 1763-1900, a death index 1916 to 1950, and more.