Williamson County permit authority

Williamson County Department of Infrastructure, County Engineer's Office; Williamson County Fire Marshal is the identified county-level authority for this profile. Confirm that the property is in its service area before filing.

Begin with the online permit gateway listed in the application guide. If the portal does not recognize the address or project type, contact County Engineer/Development Services/OSSF/Floodplain: 512-943-3330; fax 512-943-3335; Fire Marshal: 512-943-3601; general county line: 512-943-1100.

The county's OSSF guide states that the initial design review may take up to 30 days; an OSSF application is valid for one year from purchase. No fixed floodplain or Fire Marshal review time is published. A floodplain application expires one year after purchase, must remain active/open at completion, and renewal requires another fee and compliance with the then-current rules.

Floodplain projects require original signed and sealed FEMA Elevation Certificates at two stages: immediately after the foundation slab or first floor and again after final completion/grading; the application also requires the first certificate within 14 days after foundation construction. A licensed surveyor or qualified engineer/architect must certify elevation, and floodway work requires the professional engineer's no-rise certification. For OSSF inspections, the licensed installer calls 512-943-3330 and follows the scheduling prompts; most permits include inspections at two critical phases, and no system may operate until all inspections pass and the county issues its License to Operate. Homeowner-installers require prior written approval and receive a written inspection schedule. Commercial/fire-protection applicants request plan review and construction, alarm, sprinkler, underground, hood, and final inspections electronically through https://www.wilcopermits.com/.

Williamson County has not adopted Local Government Code Chapter 233 Subchapter F and does not require ordinary new residential construction in unincorporated areas to conform to a county building code; it also lacks general zoning authority and does not issue residential certificates of occupancy. The county nevertheless requires a Certificate of Compliance for structures/development outside a regulated floodplain and a Floodplain Development Permit within or adjacent to a regulated 1-percent floodplain under the Williamson County Flood Damage Prevention Order, using the December 20, 2019 FIS/FIRM and later revisions. Unincorporated public, commercial, and multifamily buildings of four or more units are reviewed by the Fire Marshal under the Williamson County Fire Code, 2018 International Fire Code with local amendments, and NFPA 72. OSSFs are regulated under the county's TCEQ-approved 2021 OSSF Order, 30 TAC Chapter 285, and applicable Edwards Aquifer rules. A floodplain-development permit is not required when the county determines development is clearly outside a special-flood-hazard area, but a Certificate of Compliance is still required unless a valid certificate was already issued on the recorded plat. The 500-year Zone X shaded floodplain is not currently regulated by FEMA or Williamson County. Ordinary unincorporated residential construction has no county structural-building permit/code requirement, although floodplain, septic, driveway, subdivision, ETJ, ESD, and other approvals may apply. The current OSSF page requires an application to install, repair, enlarge, or modify a system and publishes no blanket acreage exemption. For fire alarms, an existing device used with a replacement control panel on a true like-for-like basis does not require a Fire Marshal permit.