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Unincorporated Santa Clara County, CA Homes for Sale & Real Estate

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

Unincorporated Santa Clara County is the land in the county that lies outside every city and town, from Stanford’s campus lands and small pockets surrounded by San Jose to the hillsides, the Santa Cruz Mountains and the farm valley around San Martin. On these parcels the County of Santa Clara, not a city, controls zoning and building permits. Septic systems go through the county’s Department of Environmental Health and wells through Valley Water, and the only transfer tax is the county’s $1.10 per $1,000.

That split of authority changes how you check a property. A Los Gatos, San Jose or Morgan Hill mailing address can still put a parcel under county rules, and a city’s planning counter cannot approve work on it. This guide explains who handles what, the main unincorporated areas we could verify, rural zoning, the Williamson Act, wells and septic, hazards, tax and tenant rules, and what a seller should prepare.

Unincorporated Santa Clara County homes for sale

Unincorporated Santa Clara County market report

What “unincorporated” means for permits and services

The county’s Department of Planning and Development publishes the County Zoning Ordinance and a zoning atlas of 281 map sheets. Its online Property Explorer reports a parcel’s location, jurisdiction, general plan designation and zoning, so it is the first check for any address. Building permits for unincorporated parcels are issued by the same department.

Question	Who handles it on an unincorporated parcel
Zoning, use permits, subdivisions, accessory dwelling units	County Department of Planning and Development
Building permits and inspections	County Department of Planning and Development
Septic (onsite wastewater) approval	County Department of Environmental Health
Well construction, repair and destruction permits	Valley Water, Wells and Water Production Unit
Williamson Act contracts	Clerk of the Board keeps contracts; the Assessor values the land; Planning and Agriculture monitor compliance
Wildland fire protection on State Responsibility Area land	CAL FIRE
Transfer tax	County only, $1.10 per $1,000
Tenant displacement rules	County tenant protection ordinance (revision pending, see below), plus state law

Annexation can move a parcel into a city. Santa Clara LAFCO, the agency that sets city boundaries, explains that a 2001 state law, Government Code section 56375.3, lets cities annex qualifying islands of 150 acres or less without protest proceedings or an election. Check the parcel’s status at the time you buy, not from an old listing.

The main unincorporated areas

Islands inside city urban service areas

LAFCO defines an island, or pocket, as unincorporated land inside a city’s urban service area. These islands stay under county land use authority even though a city surrounds them. LAFCO’s island maps, dated February 27, 2020, cover 13 cities: Cupertino, Gilroy, Los Altos, Los Altos Hills, Los Gatos, Milpitas, Monte Sereno, Morgan Hill, Mountain View, San Jose, Santa Clara, Saratoga and Sunnyvale.

Since the island program began, about 82 islands covering nearly 2,000 acres and more than 18,000 residents have been annexed, LAFCO says, but many remain. A house on a city-looking street can still need a county permit, so check before you plan an addition.

Stanford lands

Stanford University occupies 8,180 acres, about half of it under County of Santa Clara jurisdiction, according to the county’s Stanford page. The Stanford University Community Plan, adopted in 2000 and amended in October 2023, and the 2000 General Use Permit govern development on those unincorporated lands.

Stanford has filed applications for a new General Use Permit with related Community Plan, zoning and development agreement changes; we found no decision date. Campus housing is a separate program with its own eligibility rules, covered in our Stanford homes guide.

San Martin and the South County valley

The county describes San Martin as a rural unincorporated community between Morgan Hill and Gilroy. Its planning area runs across the valley floor between the eastern and western hillsides, from Maple Avenue south to Masten and Fitzgerald Avenues.

Special area policies first written into the county General Plan in 1980 still apply, along with the 1995 San Martin Integrated Design Plan. A nine-member San Martin Planning Advisory Committee advises the county on major subdivisions and use permits there; our San Martin property page goes further.

North of Morgan Hill, Coyote Valley is one of the areas the county’s septic program names as having many onsite systems. Jurisdiction there depends on the parcel; see our Coyote property guide.

Hillsides and mountains

The county’s 2014 onsite wastewater program places most septic systems outside sewer service areas, across much of the South County, the eastern and western foothills and the mountains. The Lexington Basin, above Los Gatos in the Santa Cruz Mountains, is one of the named concentrations. Mountain communities on our site include Redwood Estates off Highway 17, the historic mining village of New Almaden, and Mount Hamilton east of San Jose.

Zoning basics: Agriculture, Ranchlands, Hillsides and Rural Residential

Chapter 2.20 of the County Zoning Ordinance, revised April 2024, sets four rural base districts. Their shared intent, in the ordinance’s words, is to “maintain and preserve the predominantly rural character of lands.”

District	Name	What to know
A	Exclusive Agriculture	Meant to preserve the long-term viability of agriculture; applies to land the General Plan designates Agriculture (large or medium scale) or Open Space Reserve; agricultural preservation criteria in section 2.20.050
AR	Agricultural Ranchlands	Ranch land; read the district purpose statement for allowed uses
HS	Hillsides	Hillside land, where slope-density rules in section 2.20.040 affect how many lots a parcel can yield
RR	Rural Residential	Rural home sites; in San Martin, special area policies supplement Rural Residential designations

The ordinance also has a San Martin Use Permit Areas combining district (section 3.90) for the commercial and industrial use permit areas there. Minimum lot sizes and slope-density figures vary by district and by any suffix on the zoning map, so read the parcel’s exact zoning in Property Explorer and the ordinance text rather than relying on a district name.

For a rural purchase, three questions come first: whether the parcel is a legal lot, what zoning and General Plan designation apply, and whether a contract restricts it. Our Santa Clara County rural land guide covers lot legality, access and development questions in more depth.

The Williamson Act in Santa Clara County

The county Assessor reports more than 362,704 acres under Williamson Act contracts, about 43% of the county’s land area. Contract land is assessed on its income-producing value rather than market value, and the Assessor sets those values each year from a market rent survey that owners must answer. An owner who fails to respond by April 10 risks an investigation or nonrenewal.

Term. Contracts run ten years and renew automatically each January 1 unless cancelled or a notice of nonrenewal is filed.
Nonrenewal. Once filed, nonrenewal starts the next January 1 with nine years left, and the tax rises in steps until it matches uncontracted land at the end of the term.
Who does what. The Clerk of the Board keeps the contracts and handles new contracts, nonrenewals and cancellations, while Planning and Agriculture jointly monitor that contracted land stays in agricultural use.

A buyer takes the contract with the land. Ask the seller for the recorded contract, the latest Assessor survey response and any compliance correspondence, and price the property on the use the contract allows. Our Williamson Act guide explains cancellation and compatible uses statewide.

Wells and septic: two different agencies

Septic systems: Department of Environmental Health

The county’s Local Agency Management Program for onsite wastewater, dated July 2014, estimated about 12,500 septic systems countywide from a 2012 parcel analysis. The Department of Environmental Health regulates them in unincorporated areas and administers them for the cities by agreement.

A building permit cannot be issued, or a building occupied, without the department’s approval of the system. New systems need a site evaluation with soil profiles, with percolation testing by a consultant the owner hires. Alternative systems need both a construction permit and a renewable operating permit.

We did not find a county rule requiring a septic inspection at sale, so a buyer usually orders one. Ask for the system permit, pumping records and any operating permit, and have a qualified inspector check the tank and dispersal field before you remove contingencies.

Wells: Valley Water

Valley Water, not the county health department, issues well permits countywide under its Ordinance 90-1, adopted April 24, 1990. Nobody may dig, bore, drill, deepen, modify, repair or destroy a well without a permit, and starting work without one doubles the permit fee.

An owner may not knowingly allow an abandoned well to remain on the property, and abandoned wells must be destroyed to district standards. Violations are misdemeanors.

When a property depends on a well, ask for the well permit or log, recent water quality and yield tests, and any shared-well agreement. Diamond may refer you to partners we work with; you’re free to choose any provider.

Fire, earthquake and flood

Fire. CAL FIRE’s State Responsibility Area fire hazard severity zone maps took effect April 1, 2024; much rural hillside land falls in the SRA, where CAL FIRE has primary wildland fire responsibility. Look up the parcel in CAL FIRE’s SRA viewer, and where a zone applies read our AB 38 defensible space inspection guide.
Earthquake. CGS’s EQ Zapp shows whether a parcel is in a mapped fault rupture, liquefaction or earthquake-induced landslide zone, and whether CGS has evaluated the area yet. Hillside and mountain lots raise landslide questions; new building in a mapped zone needs site-specific geologic study.
Flood. Creek-side and valley parcels can sit in FEMA flood zones; check FEMA’s flood map for the parcel and ask your lender about insurance early.

The seller’s Natural Hazard Disclosure report pulls these maps together. Read it during the inspection period, and price insurance before you commit.

Transfer tax and tenant rules

Unincorporated parcels pay only the county documentary transfer tax of $1.10 per $1,000 of value: $2,200 on a $2,000,000 sale. Ticor Title’s 2026 guide lists the county tax, the escrow fee and the owner’s title policy as seller costs by custom in unincorporated Santa Clara County, and notes that terms are negotiable. San Jose, Mountain View and Palo Alto add city taxes that do not reach county land; our Santa Clara County city transfer tax guide shows those rates.

The county has no rent cap of its own that we could find, so covered rentals fall under the state Tenant Protection Act. The Attorney General lists 8.6% as the maximum increase for Santa Clara County increases taking effect August 1, 2026 through July 31, 2027. Our AB 1482 landlord guide explains exemptions.

Eviction rules are changing. On June 2, 2026 the Board of Supervisors voted 4–1 to advance a revision of the county’s 1993 tenant protection ordinance for unincorporated areas, according to San José Spotlight and Local News Matters. The vote needed a second reading, which the California Apartment Association reported was set for June 23, 2026, with the changes taking effect January 1, 2027.

As reported, the revision extends just cause protection to many renters state law leaves out, including in single-family homes, duplexes and housing built in the last 15 years. For owner move-in, withdrawal from the rental market and demolition, it would require relocation assistance of three months’ rent or a waiver of the last three months’ rent.

We did not find the adopted text or effective date on a county source, so confirm both with the county before you buy or give notice on a rental. This is general information, not legal advice; a California landlord-tenant attorney can tell you how the county ordinance applies to a particular unit.

Selling a home in unincorporated Santa Clara County

Confirm the jurisdiction in Property Explorer and tell buyers plainly that the county, not a city, issues permits.
Gather permits for the house, additions, accessory units and outbuildings from the county, and note anything built without one.
Assemble septic and well records: the system approval, pumping history, well permit or log and recent water tests.
Disclose any Williamson Act contract and provide the recorded contract and recent Assessor survey responses.
Document access and shared systems: road maintenance agreements, easements and shared-well agreements.
Order the Natural Hazard Disclosure, and the defensible space inspection where the property is in a high fire hazard zone.
Prepare tenant records for any rented unit under AB 1482 and the county ordinance.
Price from comparable sales with the same jurisdiction, water and wastewater setup, because a septic and well property and a sewered city lot on the same road are not the same product.

Diamond is a member of C.A.R., NAR and the area MLSs, and we also reach likely buyers for rural and county parcels through our own client database and targeted off-market campaigns, following MLS rules and NAR’s Clear Cooperation policy. Our Santa Clara County seller services page covers preparation, and you can request a home valuation online.

Questions people ask

How do I know if a property is in unincorporated Santa Clara County?

Look up the parcel in the county Planning and Development Department’s Property Explorer, which shows jurisdiction, General Plan designation and zoning. Do not rely on the mailing city; islands inside San Jose and other cities stay under county authority until annexed.

Who issues building permits outside the cities?

The County Department of Planning and Development handles zoning and building permits for unincorporated parcels. Septic approval comes from the Department of Environmental Health and well permits from Valley Water.

What are the main unincorporated areas?

The ones we verified are the islands inside 13 cities’ urban service areas, the roughly half of Stanford’s 8,180 acres under county jurisdiction, San Martin, Coyote Valley and the foothill and mountain areas, including the Lexington Basin above Los Gatos.

Is there a city transfer tax in unincorporated areas?

No. Only the county’s $1.10 per $1,000 applies, which the seller customarily pays in Santa Clara County, though the split is negotiable.

Does unincorporated Santa Clara County have rent control?

We found no county rent cap; AB 1482 limits increases on covered units to 8.6% for increases taking effect August 1, 2026 through July 31, 2027. A county revision adding just cause and relocation rules beyond state law was reported to take effect January 1, 2027; confirm the final text with the county.

Who issues well permits in Santa Clara County?

Valley Water, under Ordinance 90-1 of 1990. A permit is required to drill, deepen, repair or destroy a well, and abandoned wells must be destroyed to district standards.

Is a septic inspection required when I sell?

We found no county point-of-sale septic inspection rule. Buyers usually order their own inspection, and the department’s approval is needed before new building permits on a septic property.

How does a Williamson Act contract affect a purchase?

The contract stays with the land, limits uses and keeps the property assessed on income value. Contracts run ten years and renew each January 1; after a nonrenewal notice the tax rises over the remaining nine years.

Can I build a second home or split a hillside lot?

It depends on the parcel’s zoning, General Plan designation, slope-density rules and septic capacity. Ask the county for a pre-application review before you count on more units in your price.

Are mountain properties in a fire hazard zone?

Many hillside and mountain parcels are in the State Responsibility Area, whose fire hazard maps took effect April 1, 2024. Check the parcel in CAL FIRE’s viewer and in the seller’s Natural Hazard Disclosure.

For the cities around these areas, our Santa Clara County guide compares taxes, rent rules and towns. If you are buying or selling a county parcel, talk with Diamond Real Estate Group about the address.

Sources & notes

Last reviewed October 2026 by Matthew Martinez.