Illinois County, VA
27 April 1790
Northwest Territory, St. Clair County
9 February 1801
Indiana Territory, St. Clair County
28 April 1809
Illinois Territory, St. Clair County
14 September 1812
Illinois Territory, Madison County
4 January 1817
Illinois Territory, Madison and Bond County
3 December 1818
30 January 1821
State of Illinois, Sangamon County formed. County boundaries
then included the present day Counties of Scott; Morgan; Cass; Menard; Mason; Tazewell; Logan; parts of Christian; Woodford; Macon; Marshall; McLean; and Putnam.
31 January 1823
Morgan County formed/taken away from Sangamon County. Morgan included present
day Counties of Scott; Cass and Morgan.
23 December 1825
Peoria County formed taking away Mason; Tazewell; and parts of McLean;
Woodford; Marshall; and Putnam from Sangamon County
Menard, Logan and Dane Counties
(later Christian) formed from Sangamon, with parts of eastern edge of Sangamon
being added to Macon County.
Sangamon County is now composed as it is today.