Admitted to the Union on December 3, 1818 as the 21st state. Prior to statehood, it was enumerated as Illinois Territory (became a territory in 1809).

  • 1800 federal census lost for all counties.
  • 1810 federal census extant for Randolph (southern portion of the territory) and lost for St. Clair (upper two-thirds of territory).
  • 1890 federal census lost for all counties except part of McDonough (Mound Township).
  • 1820—1940 federal censuses extant for all counties except for 1890 (see above).
Adams Alexander Bond Boone
Brown Bureau Calhoun Carroll
Cass Champaign Christian Clark
Clay Clinton Coles Cook
Crawford Cumberland DeKalb De Witt
Douglas DuPage Edgar Edwards
Effingham Fayette Ford Franklin
Fulton Gallatin Greene Grundy
Hamilton Hancock Hardin Henderson
Henry Iroquois Jackson Jasper
Jefferson Jersey Jo Daviess Johnson
Kane Kankakee Kendall Knox
La Salle Lake Lawrence Lee
Livingston Logan McDonough McHenry
McLean Macon Macoupin Madison
Marion Marshall Mason Massac
Menard Mercer Monroe Montgomery
Morgan Moultrie Ogle Peoria
Perry Piatt Pike Pope
Pulaski Putnam Randolph Richland
Rock Island Saline Sangamon Schuyler
Scott Shelby St. Clair Stark
Stephenson Tazewell Union Vermilion
Wabash Warren Washington Wayne
White Whiteside Will Williamson
Winnebago Woodford