Tex. Spec. Dist. Local Laws Code § 1030.004

Unless the district's boundaries are expanded under Subchapter H, the boundaries of the district are coextensive with the boundaries of Frio County, Texas, except that a portion of the southern boundary follows the boundary of the Frio River beginning at the intersection of the south county line and the Frio River to the point at which the boundary intersects the Leona River and follows the Leona River to the west county line.