Septic rules in Williamson County
Williamson County takes septic applications only through the MyGovernment Online site, with no email or paper, as of its June 2026 page. To see whether a property needs a septic permit, look it up in the County Address Search; if it's listed as Unincorporated or in an ETJ, it likely does. The County Engineer's Office, Department of Infrastructure, answers at 512-943-3330 or ossf@wilcotx.gov, from 3151 SE Inner Loop, Suite B, Georgetown 78626.
That office says TCEQ has authorized it to run the OSSF program for Williamson County, except areas inside the City of Austin, under the County Engineer's own On-Site Sewage Facility Rules. The fee sheet updated 9/12/25 lists a residential conventional system at $510.00, a residential non-conventional, non-aerobic one at $610.00, and a residential aerobic unit with routine maintenance required at $710.00. Commercial is $810.00 non-aerobic and $910.00 aerobic. An extra site visit is $100.00, a new or additional design review $150.00 and subdivision review $20.00 per lot.
Aerobic systems also renew their license each year at $60.00, the same fee as a transfer. Aerobic units need a maintenance contract and an affidavit, and the county posts a Homeowner Maintenance Packet. Its guide, in a March 2025 copy, says homeowners or installers may prepare the design for a standard gravity or ET system unless the site is in the 100-year floodplain or a recharge zone. For repair costs, the county's financial resources sheet, updated 2025-09-29, lists USDA Rural Development home-repair loans and grants through the state office at (254) 742-9700.
The county's rules, line by line
- Who permits septic systems
- Williamson County Department of Infrastructure, County Engineer's Office, 3151 SE Inner Loop, Suite B, Georgetown 78626; 512-943-3330; ossf@wilcotx.gov. TCEQ has authorized the office to administer the OSSF program for the county except areas inside the City of Austin.
- Governing code
- Williamson County Engineer's On-Site Sewage Facility Rules, on top of 30 TAC 285.
- Inspection at sale
- No rule found in the county's published code. The county's septic pages state no inspection rule for a sale or transfer. For an aerobic system, the license transfer to a new owner is listed at $60.00 on the fee sheet updated 9/12/25.
- Permit steps
- Applications are accepted only through the MyGovernment Online site (no email or paper). Use the County Address Search to learn whether a property needs an OSSF: an address listed Unincorporated or in an ETJ likely requires one.
- Installers and evaluators
- Residents or installers may prepare the design for standard gravity or ET systems unless the site is in the 100-year floodplain or recharge zone (guide copy of 2025-03-05).
- Still to confirm with the county
- Aerobic treatment units require a maintenance contract and an affidavit (county guide as of 2025-03-05); the aerobic license renews annually. The county financial resources sheet (updated 2025-09-29) lists USDA Rural Development home-repair loans and grants.
Septic fees in Williamson County
| Item | Amount | Note |
|---|---|---|
| Residential conventional | $510.00 | Updated 9/12/25 |
| Residential non-conventional / non-aerobic | $610.00 | Updated 9/12/25 |
| Residential aerobic treatment unit, routine maintenance required | $710.00 | Updated 9/12/25 |
| Commercial non-aerobic | $810.00 | Updated 9/12/25 |
| Commercial aerobic | $910.00 | Updated 9/12/25 |
| Extra site visit / inspection | $100.00 | Updated 9/12/25 |
| New or additional design review | $150.00 | Updated 9/12/25 |
| License renewal or transfer, aerobic | $60.00 | Updated 9/12/25 |
| Subdivision review | $20.00 | Per lot; updated 9/12/25 |
Rules and fees change every year, so confirm a line with the Williamson County Engineer's Office before you rely on it. "No rule found" means the pages and code we have say nothing on that line, which isn't the same as the county telling you there's no rule. To compare counties, use the county rules lookup.
What septic work costs
These are statewide Texas estimates from our model, so they aren't Williamson County prices; where the county posts its own permit fees, they are on this page.
| Job | Estimated range | Unit |
|---|---|---|
| Septic pumping | $300 to $600 | per visit |
| Septic inspection | $110 to $455 | per inspection |
| Drain field | $690 to $4,650 | per repair |
These are estimates, not quotes. How we estimate costs.