40 C.F.R. § 81.88
The Metropolitan Billings Intrastate Air Quality Control Region (Montana) has been renamed the Billings Intrastate Air Quality Control Region and 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 Montana: Big Horn County, Carbon County, Fergus County, Golden Valley County, Judith Basin County, Musselshell County, Petroleum County, Stillwater County, Sweet Grass County, Wheatland County, Yellowstone County.
(Sec. 301(a), 81 Stat. 490, 504; 42 U.S.C. 1857g(a) as amended by sec. 15(c)(2) of Pub. L. 91-604 )
Note: For purposes of identification, the Regions are referred to by Montana authorities as follows:
Sec.
481.168 Great Falls Intrastate Air Quality Control Region: Region II.
481.169 Helena Intrastate Air Quality Control Region: Region IV.
481.170 Miles City Intrastate Air Quality Control Region: Region III.
481.171 Missoula Intrastate Air Quality Control Region: Region I.
481.88 Billings Intrastate Air Quality Control Region: Region V.
40 C.F.R. §81.88