The official language of the State of Illinois is English.
5 ILCS 460/20
Official language
Known as the State Designations Act
The act spans §§ 5-460-1 to 5-460-95 (40 sections).
P.A. 87-273.
Official source: Illinois General Assembly. Reproduced from public-domain Illinois statutes; confirm against the official source for the current text. Not legal advice.