This record collection in Ancestry Library Edition (Ancestry LE) includes Illinois state censuses for the years 1825, 1830, 1835, 1845, 1855, and 1865. These censuses were usually enumerated in years when a federal census was not being conducted. Normally only Head of Household is mentioned by name; other persons in the household are only hash marks in various categories.

Information provided in an item record generally includes:
Name
Enumeration Date
Place of Residence
Using View Record to look at the actual census page may reveal additional information.
Censuses enumerated prior to 1855 include only 4 or fewer counties. What we must remember, however, is that Illinois only had 15 counties when it became a state in 1818, and only achieved its current total of 102 counties in 1859. So check all potential census years even if a census supposedly does not cover the county your people lived in.
You may use Ancestry LE at Central Library or any of our branches.