Hays County (Unincorporated)
Hays County Development Services
CountyMS4 Phase IIVerified 2026-03
Local Permit / Authorization
- Permit Required
- Yes
- Permit Name
- Floodplain Development Permit / Drainage Review
- Submit To
- Hays County Development Services
- Lead Time
- Plan review typically 2–4 weeks
- Application Method
- Submit via Hays County Development Services at 712 S. Stagecoach Trail, Suite 1033, San Marcos, TX 78666 or online portal at hayscountytx.com
- Fee
- Contact agency for current fee schedule
Water Quality Standards
- Impervious Cover Limit
- Portions of unincorporated Hays County are within the Edwards Aquifer Recharge and Contributing Zones — EAA permit required for development over the aquifer; impervious cover caps apply as required by EAA rules
- On-Site Treatment Required
- No
- Detention Required
- Yes
- Detention Standard
- Detention required to limit post-development peak flows to pre-development levels for 2-, 5-, 10-, 25-, and 100-year storms per Hays County Drainage Design Standards; applies in unincorporated areas and ETJs where cities lack their own standards
- Turbidity Standard
- No numeric NTU limit; discharges must comply with TCEQ TXR150000 and not degrade Blanco River, Onion Creek, Plum Creek, or San Marcos River
Local SWPPP / Drainage Plan
- Local Plan Required
- Yes
- Plan Name
- SWPPP per TCEQ TXR150000; drainage report required for county permits
- PE Stamp Required
- Yes
Drainage study prepared by a Texas PE required for development permits in unincorporated Hays County. The county is experiencing explosive growth as the fastest-growing county in Texas. Edwards Aquifer recharge and contributing zones cover significant portions of the county. The Blanco River and Onion Creek have a history of catastrophic flash flooding. County drainage standards adopted in response to rapid growth may be less developed than city standards — verify current requirements with Hays County Development Services.
Local Inspection Requirements
- Requirements
- Hays County Development Services inspects development in unincorporated areas. County capacity has been stressed by rapid growth.
- Inspector Qualification
- No county-specific certification required beyond TCEQ SWPPP requirements
Special Overlay Zones
Edwards Aquifer Recharge Zone
Trigger: Development over the Edwards Aquifer Recharge Zone in unincorporated Hays County (primarily the western, higher-elevation areas)
Restriction: EAA permit required; impervious cover limited to 15%; water quality controls and karst protection required; direct discharge to sinkholes, caves, or other recharge features prohibited
Blanco River Floodplain
Trigger: Development within FEMA-mapped floodplain along the Blanco River
Restriction: Floodplain development permit required from Hays County Floodplain Administrator; the Blanco experienced unprecedented flooding in May 2015 (Memorial Day flood — 40+ feet rise in Wimberley); current FEMA maps may understate actual flood risk; use conservative freeboard
Onion Creek Floodplain
Trigger: Development within FEMA-mapped floodplain along Onion Creek in the eastern, lower-elevation parts of the county
Restriction: Floodplain development permit required; Onion Creek has experienced repeated major flash floods; FEMA has remapped and bought out flood-prone properties; use current effective maps with conservative safety margin
City ETJ Areas
Trigger: Development in the Extraterritorial Jurisdiction of Kyle, Buda, San Marcos, Wimberley, or other Hays County cities
Restriction: City ETJ review authority may impose city standards even in unincorporated areas; verify ETJ boundaries and applicable standards with the relevant city before submitting county permits
Design Manual
- Manual Name
- Hays County Drainage Design Standards
Official Resources
Jurisdiction Notes
Hays County has been the fastest-growing county in Texas and consistently one of the fastest-growing in the nation, driven by Austin tech sector spillover into the I-35 corridor cities of Kyle, Buda, and San Marcos, and the FM 1626/Mopac South corridor. This entry covers unincorporated Hays County. The county's growth has significantly stressed its development services capacity. The Edwards Aquifer, Blanco River, and Onion Creek create a complex regulatory environment. The May 2015 Memorial Day flood devastated Wimberley (12+ deaths) and revealed the extreme flash flood hazard of the Hill Country rivers flowing from the Edwards Plateau.
Remember: These local requirements are in addition to the TCEQ state construction permit. Both must be satisfied before breaking ground.
Disclaimer: This information is provided for general reference only. Always verify requirements directly with Hays County Development Services and the agency website before beginning construction.