40 CFR § 81.262 - North Central Illinois Intrastate Air Quality Control Region.

The North Central Illinois Intrastate Air Quality Control Region consists of the territorial area encompassed by the boundaries of the following jurisdictions or described area (including the territorial area of all municipalities (as defined in section 302(f) of the Clean Air Act, 42 U.S.C. 1857h(f)) geographically located within the outermost boundaries of the area so delimited):

In the State of Illinois: Bureau County, La Salle County, Lee County, Marshall County, Putnam County, Stark County.