Use the U.S. Code citation form

Error²Federal courts, Illinois courts21st and 22nd editions

“42 U.S.C. § 1983”, not “42 USC § 1983”: each letter takes a period and adjacent capitals close up, and an annotated edition adds its publisher and year.¹

1. 1R. 12.3 Current Official and Unofficial Codes; R. 6.1(a) Spacing; R. 12.9.1 Internal Revenue Code; R. 12.3.1(d) Publisher, editor, or compiler; B12.1.1 Federal Statutes. Tables: R. 12.1 Basic Citation Forms.
2. 2An error: the rule in note 1 allows one form, and this is not it.