40 CFR § 81.258 - Northwest Iowa Intrastate Air Quality Control Region.

The Northwest Iowa 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 Iowa: Buena Vista County, Calhoun County, Cherokee County, Clay County, Dickinson County, Emmet County, Ida County, O'Brien County, Osceola County, Palo Alto County, Pocahontas County, Sac County.