Here is an explanation about the various nonpopulation schedules. http://www.us-census.org/research/other.htm For Illinois, the extant 1850, 1860, 1870, and 1880 schedules (originals) are at the Illinois State Archives and can be ordered on interlibrary loan from a variety of institutions through your local library or the Family History Center near you. I believe the majority of schedules are extant for Illinois.