Septic Systems and OSSF Rules in Grayson County, Texas

The 2021 half-acre order: an exception, not a blanket rule

In August 2021, the Grayson County Commissioners Court passed an order modifying the county's On-Site Sewage Facility rules to allow half-acre lots in certain circumstances -- a meaningful departure from the larger minimum lot sizes that typically apply to septic-served residential lots in Texas. But this isn't a blanket rezoning down to half acres: the order works through a case-by-case approval process, where the Commissioners Court (or, for an individual application, the county's TCEQ-licensed Designated Representative) has to sign off on a specific half-acre or larger lot before an OSSF permit for it can be authorized, and the applicant still has to satisfy every other TCEQ and county technical requirement that would apply to a larger lot. In practice, that means a listing advertising a half-acre unincorporated Grayson County lot as septic-ready should not be taken at face value -- confirm with Development Services whether that specific lot has actually received the required sign-off, rather than assuming the 2021 order makes half-acre septic lots routine countywide.

The 2-acre rule for a lot with both a well and a septic system

Separately from the half-acre exception process, Grayson County applies a standing minimum lot size of 2 acres to any parcel that will carry both a private water well and an OSSF on the same tract -- a common configuration for rural acreage that isn't on a public water system. This 2-acre figure sits on top of, not instead of, the setback distances required under 30 TAC 285.91(10) Table X (the statewide table governing distances between a septic system's components and property lines, wells, and water bodies). For a buyer looking at a smaller unincorporated tract specifically because it's inexpensive, this is one of the first things worth checking: a 1-acre or half-acre lot that needs to support both its own well and its own septic system generally will not qualify under Grayson County's rules, regardless of how the setback math on that specific lot might otherwise work out.

What to verify before buying a smaller Grayson County tract for septic use

1. If the lot is under 2 acres, confirm directly with Grayson County Development Services whether it has already received the specific Commissioners Court/Designated Representative sign-off required under the 2021 half-acre order -- don't assume a seller's or agent's representation is current.
2. If the plan is to serve the home with both a private well and an OSSF on the same lot, confirm the lot meets the 2-acre minimum before relying on it for that configuration -- a lot that's part of a public water system may not need to meet this specific threshold, but confirm that status directly rather than assuming it.
3. Budget for a licensed site evaluation (soil and setback analysis under 30 TAC 285.91) regardless of lot size -- the county's local rules narrow what's allowed, but they don't replace the underlying state technical requirements.
4. Ask Development Services directly about current OSSF permit fees and processing timelines, which this research did not independently verify to a specific current dollar figure.