Use the place’s citation abbreviation

Error²Federal courts, Illinois courts21st and 22nd editions

Citation abbreviations for places are their own set, neither postal codes nor the longer newspaper forms: “N.D. Ill.”, never “N.D. IL”; “Cal.”, never “Calif.”.¹

1. 1R. 10.4 Court and Jurisdiction; B10.1.3 Court and Year of Decision. Tables: T10 Geographical Terms; T10.1 U.S. States, Cities, and Territories.
2. 2An error: the rule in note 1 allows one form, and this is not it.