City Limits vs. County
Much of Waller County Is Unincorporated — Rules Differ Outside City Limits
Large portions of Waller County sit outside any city, which means fewer zoning restrictions but also fewer services — and cities can still regulate land just beyond their borders.
Texas cities have an Extra Territorial Jurisdiction, called an ETJ. This is a zone of land outside the city limits where the city can control subdivision plats and some development rules, but not zone the land. If you buy land in the ETJ of Katy, Waller, or Hempstead, you may face some city rules even though you are not inside city limits.
Fully unincorporated land — outside both city limits and the ETJ — has even fewer rules. There is generally no county zoning in Texas. You might be able to build or operate things that would not be allowed inside a city. But you may also be responsible for your own water well and septic system. Check with Waller County and the relevant city before you build.
Source to confirm: Waller County Official Website