Accessory Structures in Williamson County, TX (2026)

3 county-level rules, plus city-specific rules for 1 city in Williamson County, Texas.

Verified from official government sources

Note: These county rules apply to unincorporated areas of Williamson County. If you live within an incorporated city, that city's own rules apply: see the city list below.

ADU Rules

Texas counties cannot zone, so unincorporated Williamson County sets no ADU size, setback, or occupancy limit. An accessory dwelling with plumbing requires an on-site sewage (OSSF) permit under Health & Safety Code Chapter 366.

Williamson County ADU / Accessory Dwelling Rules

Few Restrictions

Tex. Health & Safety Code §366.051(a)

A person must hold a permit and an approved plan to construct, alter, repair, extend, or operate an on-site sewage disposal system.

Full ordinance details →Official source ↗

Garage Conversions

Unincorporated Williamson County neither zones nor permits garage conversions. Converting a garage into living space with a bathroom triggers an on-site sewage (OSSF) review under Health & Safety Code Chapter 366.

Williamson County Garage Conversion Rules

Light Restrictions

Tex. Health & Safety Code §366.051(a)

A person must hold a permit and an approved plan to construct, alter, repair, extend, or operate an on-site sewage disposal system.

Full ordinance details →Official source ↗

Tiny Homes

A tiny home on wheels is titled as a travel trailer under Texas Transportation Code Section 501.002 and is not used as a permanent dwelling. A tiny home on a foundation with plumbing needs an OSSF septic permit.

Williamson County Tiny Home & Small Dwelling Rules

Few Restrictions

Tex. Transp. Code §501.002(30)

is designed primarily for use as temporary living quarters in connection with recreational, camping, travel, or seasonal use; ... is not used as a permanent dwelling

Full ordinance details →Official source ↗

Accessory Structures by City in Williamson County

1 cities in Williamson County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.

Cedar ParkPop. 77,595

6 verified rules • ADU Impact Fees, ADU Owner Occupancy

All Williamson County ordinances

See every category we cover for Williamson County: parking, noise, fences, fires, animals, pools, and more.

Williamson County Ordinance Hub →