City Limits & ETJ
Much of Fort Bend County is unincorporated — rules differ outside city limits
Outside city limits, county rules apply; inside city limits or a city's ETJ, additional city rules may also apply.
Fort Bend County has several cities, including Sugar Land, Missouri City, Rosenberg, and Richmond. Land outside those city limits is called unincorporated. County rules — not city rules — apply there.
Texas cities can also control a strip of land just outside their limits. This is called an ETJ, or Extraterritorial Jurisdiction. In fast-growing Fort Bend, the ETJ matters for things like how you subdivide land and what permits you need to build.
If you are buying land or building outside a city, check with Fort Bend County's planning department. Ask if the property is inside any city's ETJ. Rules for septic systems, water service, and building can be very different depending on where you are.
Source to confirm: Fort Bend County – County Regulations