Nine local rules sit on top of TCEQ’s statewide code in Collin County, and most of them aren’t about digging a hole; they are about paperwork. A maintenance provider who visits an aerobic system, routine or in response to a complaint, has seven days to send the owner written notice, by door hanger, mail, or email, stating the date, the time, what was found, and any follow-up needed. A homeowner who wants to maintain their own aerobic system needs, at minimum, a Class D Wastewater License, must file an annual letter of intent with Development Services, and must submit test results three times a year. Any non-residential system, or a residential one that also takes wastewater from a non-residential source, needs an annual BOD test on file with the county. None of that is required by the state rules the county otherwise adopts wholesale; Collin County Order No. 2008-187-03-11 added it.
That order, approved by Commissioners Court on March 11, 2008, also incorporates 30 TAC Chapters 285 and 30 “and all future amendments and revisions thereto,” so the county’s baseline updates automatically when the state’s does. The nine local amendments in Section 10 are what sit on top of that baseline. Two of them set lot-size minimums tied to specific dates rather than a blanket rule: a lot platted for public-water service after the county’s original 1983 order needs at least one usable acre, and a lot platted for an individual water system after the 1997 order needs one and a half. Only a registered sanitarian with a site-evaluator certification, or a registered engineer, may do the site evaluation or the design. Maintenance inspections on aerobic systems run every four months, with the interval defined as 120 to 130 days, and every surface-irrigation spray head must be a subsurface pop-up type. The county’s adopted fee schedule for the year beginning October 2025 prices a new residential system at $310, or $335 with a maintenance contract, $10 of either going to the state; the 2011 application packet printed the same two figures.
Almost nothing built here is a standard trench. TCEQ’s 2025 report counts 620 systems authorized by the county’s own agent: 428 surface irrigation, 94 drip, 94 low-pressure dosed, 3 evaporation beds, one other, zero standard trench or bed. In 2024, it ran the same way: 665 authorized, and 499 of them were surface irrigation. The soil explains the pattern for most of the county: Soil Data Access rates 30 of the 40 map units carrying a septic interpretation in the TX085 survey area “Very limited” for a standard absorption field, on soils named Houston Black, Austin, and Burleson clay among others, all Blackland Prairie series with slow percolation as the limiting feature on 26 of the 30. The other limiting factor, less common in the flatter counties this directory has covered so far, is shallow depth to bedrock, the dominant problem on nine map units named for the Eddy and Stephen soils that form over chalk in the county’s rangier terrain.
Collin County Development Services in McKinney is the authorized agent for the county outside its cities, which per TCEQ’s registry covers everywhere except Dallas and Murphy (which route to other authorities) and five towns and cities with their own programs: Fairview, Farmersville, Frisco, Nevada, and Royse City. Lucas keeps its own line in that registry but is listed as administered by the county rather than running a separate program. The Texas permit authority table lists all of them. Collin County’s population reached 1,297,179 in the Census Bureau’s July 2025 estimate, up 42,966 in a single year and 231,000 since its April 2020 base, growth that keeps this list of independent city programs from staying a footnote for long.
Outside Fairview, Farmersville, Frisco, Nevada, and Royse City, Collin County Development Services issues septic permits in Collin County: 4690 Community Ave., McKinney, (972) 548-5585. Homeowners maintaining their own aerobic system under a maintenance contract file directly with that office.
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New installs and major repairs need a permit from the local authorized agent — usually the county, sometimes a city — and the rules that bind are the local ones.
This county’s full guide is still in production — the authority contact shown here is the official source in the meantime.
Four things decide what you can build and what it costs: zoning, environmental protections, power for aerobic systems, and the ground itself. We publish each one only where we have checked it — and say so plainly where the answer is “same as the rest of Texas”.
Zoning & land use
Collin County sets a lot-size floor that state rules do not. A lot divided between 1983 and 2008 must start at one acre, or 1.5 acres where the property has a water well. A lot divided in 2008 or later must have one usable acre — usable meaning usable for the disposal area, excluding most easements and ponds — or 1.5 acres with a well. A lot made smaller than that after those dates is ineligible for a septic system.
Nothing in Collin County changes this.
Texas adds a separate approval path over the Edwards Aquifer recharge, transition and contributing zones, where TCEQ requires an Edwards Aquifer Protection Plan under 30 TAC Chapter 213. Elsewhere the Chapter 285 rules stand on their own.
The dominant constraint here is clayey subsoil that water moves through too slowly (78.5% of rated soils), followed by bedrock close to the surface (17.3%). NRCS rates 86.6% of rated ground very limited for a standard soil absorption field, 15.9% for subsurface drip and 13.4% for surface application with disinfection. Where a conventional field will not pass, surface application is usually the route that does.
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