40 C.F.R. § 81.94
The Shreveport-Texarkana-Tyler Interstate Air Quality Control Region (Arkansas-Louisiana-Oklahoma-Texas) 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 Arkansas: Columbia County, Hempstead County, Howard County, Lafayette County, Little River County, Miller County, Sevier County.
In the State of Louisiana: Avoyelles Parish, Bienville Parish, Bossier Parish, Caddo Parish, Claiborne Parish, De Soto Parish, Jackson Parish, Lincoln Parish, Natchitoches Parish, Rapides Parish, Red River Parish, Sabine Parish, Vernon Parish, Webster Parish, Winn Parish.
In the State of Oklahoma: McCurtain County.
In the State of Texas: Anderson County, Bowie County, Camp County, Cass County, Cherokee County, Delta County, Franklin County, Gregg County, Harrison County, Henderson County, Hopkins County, Lamar County, Marion County, Morris County, Panola County, Rains County, Red River County, Rusk County, Smith County, Titus County, Upshur County, Van Zandt County, Wood County.
40 C.F.R. §81.94