Denton County permits center on unincorporated work; the cities (Denton, Frisco, Flower Mound, Lewisville, Little Elm, Highland Village) own their permit operations.
How this fits with the state
The state authority here is Texas Department of Licensing and Regulation; Texas State Board of Plumbing Examiners. The county file does not replace that — it adds the permit office, local overlays, and the actual filing path.