First Judicial Circuit (Illinois)
When Abraham Lincoln entered the Illinois General Assembly in December 1834, the First Judicial Circuit in central Illinois consisted of Calhoun, Greene, Macon, Macoupin, McLean, Morgan, Pike, Sangamon, and Tazewell counties. The circuit's population was concentrated in Sangamon and Morgan counties. In 1835, the legislature removed Pike County from the First Judicial Circuit; and in 1837, added Livingston and Cass counties.
Lincoln traveled the First Judicial Circuit as a lawyer from 1837 to 1839, when the legislature removed Sangamon County and redefined the circuit as Calhoun, Cass, Dane, Greene, Jersey, Macoupin, Morgan, Pike, and Scott counties. In 1841, the First Judicial Circuit shifted to southwest-central Illinois when the legislature redefined the circuit as Cass, Calhoun, Greene, Jersey, Macoupin, Morgan, Pike, and Scott counties.
"An Act Supplemental to the Several Acts Regulating the Supreme and Circuit Courts of this State,” 16 February 1831, Laws of Illinois (1831), 45; An Act Dividing the State into Judicial Circuits; An Act to Establish the County of Livingston; An Act for the Formation of the County of Cass; An Act Dividing the State into Judicial Circuits; An Act to Create and Establish the County of Jersey; An Act to Establish the Counties of Menard, Logan, and Dane; An Act to Establish Circuit Courts.