40 CFR § 81.18 - Metropolitan St. Louis Interstate Air Quality Control Region.

The Metropolitan St. Louis Interstate Air Quality Control Region (Missouri-Illinois) is revised to consist 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: Bond County, Clinton County, Madison County, Monroe County, Randolph County, St. Clair County, Washington County.

In the State of Missouri: Franklin County, Jefferson County, St. Charles County, St. Louis City, St. Louis County.