Building permits, zoning and septic rules in Collin County, Texas

Unincorporated Collin County requires a development permit for residential and commercial projects that disturb ground or add footprint, including new homes, additions, pools, fencing, grading, filling and new ponds¹. Extensive dwelling remodels that add a bedroom or double the structure value also require permitting; re-roofing, roof-mounted solar, new electrical service on an existing structure, and water-heater or AC replacements do not¹. The current development fee is $75, matching the FY2026 schedule; the FY2025 schedule listed $50 for new construction^4,5,6. Apply through the Citizen Self-Service Portal: paper applications are not accepted, invoices generally arrive in 2–4 business days, and review starts after payment and may take up to 30 days⁷. Inside Prosper and Royse City, which reaches into Collin County from Rockwall County, municipal offices handle building permits^8,9. County septic permitting applies outside city limits; Royse City’s Building Inspection Department receives OSSF applications inside that city^2,10.

Collin County Development Services is the county development-permit office; reach it at 4690 Community Ave., McKinney, Texas, 75071, or (972) 548-5585¹. New residential dwellings and substantial remodels or additions require a qualified third-party inspector and at least 3 inspections: foundation before concrete, framing and mechanical systems before drywall, and completion; manufactured homes are excluded¹. The builder must submit passing-final-inspection notice to Development Services and the owner, if different from the builder, within 10 days¹. Commercial fire-code inspections go through the Fire Marshal’s Office under the 2021 International Fire Code and local amendments¹¹. The county building-code document also lists 2009 commercial building, mechanical, plumbing, electrical and fuel-gas codes; residential structures must follow the County Seat’s adopted codes, so ask Development Services which residential edition applies¹². Public pools must follow the most recent IBC and residential pools the most recent IRC¹². Public Works handles culvert, driveway and right-of-way inspections¹.

Unincorporated Collin County has no general zoning, with exceptions for sexually-oriented businesses, salvage and junk yards, and animal slaughter operations¹. The county does not set home-size, lot-size, setback, lot-coverage or height limits by zoning, or restrict RVs, tiny homes, manufactured homes or accessory dwellings by zoning³. Prosper sets its own zoning, as do Richardson, which reaches into Collin County from Dallas County, and Royse City, which reaches in from Rockwall County^13,14,15. Septic authority is separate: Development Services serves land outside city limits, and another authorized agent may serve city addresses². ETJ land remains in county permitting jurisdiction but may face city subdivision requirements; county OSSF suitability review still applies where a city has ETJ platting authority^1,16. Land divisions, re-subdivisions and combinations must follow county subdivision regulations where Collin County is the platting authority, unless exempt¹⁶.

Collin County Development Services issues OSSF permits outside city limits and applies a county Court Order stricter than the state minimum². The published residential OSSF fee is $310 without maintenance or $335 with maintenance; review of existing septic is $50⁴. Repairs or upgrades affecting 50% of a system require permitting as a new OSSF⁴. Lots divided between 1983 and 2008 need at least 1 acre, or 1.5 acres with a water well; lots divided in 2008 or later need 1 usable acre, or 1.5 acres total with 1 acre usable if there is a well². Ask Development Services about exact boundary dates in 1983 or 2008². Only about 1% of county soils are rated free of severe limitations for conventional septic drain fields, making a site evaluation essential before choosing a system¹⁷. For a new structure connecting to a new OSSF, apply for the development permit first; staff send the associated OSSF application through your portal rather than requiring separate applications². An OSSF permit expires after 365 days of inactivity².

Collin County does not restrict RV, tiny-home or manufactured-home occupancy on unincorporated land through general zoning³. A tiny home that disturbs ground or adds footprint still needs a county development permit, and a new or altered septic system outside city limits needs a county OSSF permit^1,2. We could not confirm whether alternative off-grid sanitation is allowed or whether a general private-well permit is required; ask Development Services before choosing either for a parcel¹. A planned water well also changes the county’s septic lot-size requirements, so settle the water source before relying on a lot’s acreage².

1. Confirm city-limit and ETJ status with Development Services: county development permitting applies to unincorporated land, including ETJ property, where city subdivision requirements may also apply¹.
2. Arrange a septic site evaluation before committing to a home layout; the county’s OSSF acreage requirements vary by division date and water-well presence².
3. Apply online for the development permit before ground disturbance; the development fee is $75, and staff send the associated OSSF application if the new home will connect to a new system^1,2,4.
4. Contract a qualified third-party inspector for foundation, framing/mechanical and final inspections; submit passing-final-inspection notice within 10 days¹.
5. For a driveway onto a state highway, obtain a TxDOT permit using Form 1058; Public Works handles county culvert, driveway and right-of-way inspections^1,18.

Before buying unincorporated Collin County land, verify septic suitability and the lot’s division date: county OSSF acreage requirements can prevent a small lot from supporting a new system². Only about 1% of county soils are rated free of severe conventional-drain-field limitations, so do not choose a system from acreage alone¹⁷. County farmland value is about $13,066 per acre and typical home value about $486,570; these countywide figures do not price a particular parcel¹⁷. The effective property-tax rate is about 1.7%, with a median annual bill around $7,432 and typical annual home-insurance premium around $3,041¹⁷. Confirm subdivision and ETJ requirements before dividing or combining land, since exemptions and the platting authority depend on the property¹⁶.