City vs. County Rules
Many Denton County addresses are inside a city's planning zone, not the city itself
Texas cities have an extraterritorial jurisdiction — a buffer zone outside city limits — where they can regulate subdivisions and plats even if you pay county taxes.
In Texas, a city can claim a planning zone that reaches beyond its actual city limits. This zone is called an extraterritorial jurisdiction, or ETJ. Think of it as a buffer ring around the city. Cities like Denton, Frisco, and Lewisville in Denton County have large ETJs. If your land is inside an ETJ, you still pay county taxes — but the nearby city may control how your land can be divided or developed.
When you build in an ETJ, you follow the stricter of the city's rules or the county's rules. Getting a plat approved may require sign-off from both the city and the county. Before you buy rural land or plan any construction, check the Denton County GIS map and talk to Denton County Development Services.
Source to confirm: Denton County — ETJ Verification