Grayson County
septic services.

Texas law famously exempts septic systems on tracts over 10 acres from permitting requirements. Not in Grayson County. The county’s OSSF order requires a permit, authorization to construct, and inspection for every residential or commercial system — new, altered, extended, or repaired — “regardless of the size of the tract of land.” That’s the opening move in the most prescriptive septic order among the counties we’ve profiled, and anyone shopping land between Sherman, Denison, and the Lake Texoma shore should read it before closing.

The order’s centerpiece: any lot under 2.5 acres must use aerobic treatment — no conventional system, period. Minimum lot sizes stack on top: 1.5 acres per structure without public water (1 acre if every system is subsurface drip), 1 acre with public water (half-acre all-drip). A public sewer within 100 feet? You connect, absent County Engineer sign-off. Even self-maintenance is gated: owners may service their own aerobic units only after passing a county-approved course and signing an agreement — and forfeit the privilege by failing to submit reports. RV parks get their own regime: four or more RVs means aerobic treatment with no surface spray at all, a trash tank per five spaces, a density capped at about seven RVs per acre, and a design flow of at least 80 gallons per day per space. Little of this is guesswork for the county’s engineers — it’s written down, and we cite it directly.

Why so strict? Look at the map. The county’s north drains straight into Lake Texoma and the Red River through acidic Post Oak sands and loams; the south runs Blackland clay toward Trinity River tributaries. Sandy soils move water — and poorly treated effluent — quickly toward a lake ringed with septic-dependent communities such as Pottsboro, Preston, and Sherwood Shores. The permit ledger shows the order at work: 774 systems authorized in 2024 (15th statewide, on a county of 136,000), 632 of them — 82 percent — aerobic surface-irrigation units, exactly what the 2.5-acre rule predicts. The decade total: 6,366.

If that sounds like a county where the permit guide earns its keep, it is. Owners should also understand aerobic contract duties — the county actively polices reporting — and keep pump-out schedules documented for resale.

Grayson County office: 100 W. Houston St., Suite G-3, Sherman — (903) 813-4247, M–F 8–12 and 1–5. Permit walkthrough here.