40 C.F.R. § 81.74
The Northwest Pennsylvania-Youngstown Interstate Air Quality Control Region (Pennsylvania-Ohio) is redesignated 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 Ohio: Ashtabula County, Mahoning County, Trumbull County.
In the State of Pennsylvania: Cameron County, Clarion County, Clearfield County, Crawford County, Elk County, Erie County, Forest County, Jefferson County, Lawrence County, McKean County, Mercer County, Potter County, Venango County, Warren County.
40 C.F.R. §81.74