Source Information Illinois, U.S., State Census Collection, 1825-1865 [database on-line]. Lehi, UT, USA: Operations Inc, 2008.
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About Illinois, U.S., State Census Collection, 1825-1865

This database contains state censuses for the years 1825, 1830, 1835, 1845, 1855, and 1865. Information available for an individual will vary according to the census year and the information requested on the census form. Details for each record typically include: name, enumeration date, and enumeration place. These censuses generally only recorded the names of the heads of household, though other individuals in the household were numbered in age and race categories. See the browse menu for a complete list of counties included for each census year.

Note: This database also includes 1865 agricultural schedules for several counties (McHenry–Ogle).

About State Censuses:

State censuses were often taken in years between the federal censuses. In some places, local censuses were designed to collect specific data, such as the financial strengths and needs of communities; tallies of school-age children and potential school populations to predict needs for teachers and facilities; censuses of military strength, cavalry horse resources, and grain storage; enumeration for revenue assessment and urban planning; and lists to monitor African Americans moving into the northern cities.

Taken from Szucs, Loretto Dennis, "Research in Census Records." In The Source: A Guidebook of American Genealogy, ed. Loretto Dennis Szucs and Sandra Hargreaves Luebking (Salt Lake City: Ancestry, 1997).