Cities | Ontario

Ontario, California Multiplex Rules 2026: Zoning, Lot Sizes, ADUs, SB 9, Multiple-Family Homes, Airport Zones, Specific Plans and Fees

This guide covers the City of Ontario, California, a city of 187,013 people in San Bernardino County. The Canadian province of Ontario is a separate place with its own laws. The City's zoning rules are the Ontario Development Code, which the City posts on its Development Code page. Three facts matter for a project here. Every residential zone has a minimum density as well as a maximum, and attached homes start at the MDR-11 zone. The City's two-unit section is narrower than the state statute in seven places. And an airport compatibility plan and 52 specific plans change the rules on the land they cover. This page summarizes the ways to build two, three, four or more homes on an Ontario lot. The seven guide pages below cover each topic in depth.

Ontario Guide Pages

Start With State Law

Four state laws set the minimum Ontario must allow on a house lot or a small site. SB 9 (2021) allows two main homes on a lot in a single-family zone, a split into two lots, or both, approved by staff with no hearing. ADU law sets the accessory dwelling units (ADUs), second homes on a lot, and junior ADUs a city must allow; a junior ADU is a unit of 500 square feet or less inside a house. SB 684 and SB 1123 allow maps of up to 10 lots with 10 homes. The state density bonus gives extra homes to projects that include affordable homes.

California cities are either general law cities, which follow the state's general rules for city government, or charter cities, which have a charter approved by their voters. This guide did not open a City document that states which one Ontario is. Four state housing laws say in their own text that they cover both kinds. Government Code 65852.21 and 66411.7 define a local agency as a city "whether general law or chartered," and the ADU statutes use the same words. Government Code 65918 says of the density bonus, "The provisions of this chapter shall apply to charter cities." The Housing Accountability Act says it "shall be applicable to charter cities."

The City has written three of these laws into its code: ADUs in Section 5.03.010, two-unit projects in Section 5.03.403, urban lot splits in Section 6.08.060 and the density bonus in Section 6.01.010.H. A search of the ten code files saved for this guide found no mention of the small-lot map statute or of SB 79, the 2025 law on housing near transit stops. HCD, the state housing department, says in its SB 79 advisory that the law's upzoning provisions "will take effect on July 1, 2026, in Alameda, Los Angeles, Sacramento, San Francisco, San Mateo, Santa Clara, and San Diego Counties." San Bernardino County is absent from that list.

Ontario in Numbers

The US Census Bureau's Vintage 2025 city file estimates 187,013 people in the City of Ontario on July 1, 2025. The 2020 estimates base is 175,262, so the city grew by 11,751 people, or 6.7 percent (VanPlex arithmetic), and the 2024 estimate is 185,669. In that file Ontario is the 25th largest city in California, after Glendale (187,160) and ahead of Elk Grove (185,007). San Bernardino County has 2,224,091 people, so the City holds 8.41 percent of them (VanPlex arithmetic: 187,013 divided by 2,224,091).

A City staff report of August 18, 2026 describes the city as "approximately 50 square miles (32,022 acres) of land" and "substantially built-out with a mix of residential, commercial, industrial, agricultural, airport, recreational, and institutional/public land uses." The same report still cites a 2022 population estimate of 179,516 and a rank of 26th; the Census figure above is three years newer. The Development Code gives the scale of the rules: eight residential zones, seven mixed-use zones, a density range from 2 homes per acre to 75, 52 specific plans and 15 Planned Unit Developments. The City's housing plan, the Housing Element of The Ontario Plan, was not read for this guide, so no housing target or permit count is given here.

The Ways to More Homes Compared

Sources: Ontario Development Code 5.03.010, 5.03.403 and Table 5.02-1, 6.01.010, 6.01.020, 6.01.035 and 6.08.060, 4.02.025 and Table 2.02-1; Gov. Code 65915 and 66499.41.

Zones That Allow Homes

Section 5.01.005 lists eight residential zones, and the number in each name is its top density: AR-2, RE-2, RE-4, LDR-5, MDR-11, MDR-18, MDR-25 and HDR-45. The Land Use Matrix prohibits multiple-family dwellings in the first four, and the code defines that use as "Two or more attached dwelling units," so the matrix prohibits a duplex on an LDR-5 lot. Each zone also has a minimum: "A residentially zoned lot shall be developed at no less than the minimum number of dwelling units allowed within the specified density range." A 10,000 square foot lot yields two homes in MDR-11, three or four in MDR-18 and five in MDR-25 by VanPlex arithmetic. Seven mixed-use zones allow 14 to 75 homes per acre. See the zoning districts page.

Lot Sizes and Dividing Land

A traditional house lot needs 7,200 square feet and 60 feet of width in LDR-5 and 5,000 square feet and 50 feet in the MDR zones. A division into 4 or fewer lots needs a parcel map and 5 or more a tract map; the Planning Commission decides tentative maps and the City Council approves final maps. Ontario's own code has a small-lot option designed for infill: a Small Lot Infill Subdivision may create lots with "a minimum area of 480 SF and a minimum lot width of 16 FT," up to 45 homes. The City's SB 9 lot split section covers LDR-5 lots of at least 2,400 square feet and asks each new lot for "frontage on the public street right-of-way of at least 20 FT." See the lot size and subdivisions page.

House Lots: ADUs and SB 9

Section 5.03.010 sorts ADUs into two classes. Class 1 units are the ones state law makes a city approve: a converted ADU, a junior ADU, a detached ADU of up to 800 square feet, and ADUs on multiple-family lots, now "up to 8 detached ADUs on a lot with an existing multiple-family dwelling." Class 2 units may be larger, "850 SF of interior livable space for a studio or one-bedroom unit and 1,000 SF of interior livable space for a unit with 2 or more bedrooms," and must meet City standards on front setback, lot coverage, design, windows and screening plants. Every ADU is decided with no hearing: "The City must approve or deny an application to create an ADU or JADU within 60 days from the date that the City receives a complete application."

The City's SB 9 section limits each home in a two-unit project to between 500 and 800 square feet, limits applicants to individual owners, and requires the owners to live on the lot. The state statute has been amended since, and it now bars standards "that do not apply uniformly to development within the underlying zone." Ask the City which limits it applies today. See the ADUs and SB 9 page.

Three or More Homes

Multiple-family homes are permitted in the MDR zones and HDR-45, with a project area of 10,000 square feet in the MDR zones and 1.0 acre in HDR-45 and heights of 35, 45, 60 and 75 feet. Section 4.02.025 requires Development Plan approval for "The development of 3 or more dwelling units on a single lot," and the Planning Commission decides those plans. Projects of more than 3 homes add open space of 310 to 500 square feet per home. In April 2025 the Council adopted Objective Development and Design Standards for multiple-family and mixed-use housing, with three building types and six architectural styles. The density bonus section applies to projects with "a minimum of 5 dwelling units." See the three or more homes page.

Parking, Setbacks and Height

An LDR-5 house needs a 20-foot front setback on a collector or local street and 30 feet on an arterial street, 5-foot side setbacks, and a rear setback of 10 feet for the first floor and 20 feet above it. Height is 35 feet for houses in every zone, and buildings may cover 50 percent of an LDR-5 lot. Table 6.03-1 asks a traditional single-family dwelling for "2 spaces per dwelling within a garage" and a multiple-family home for 1.5 to 2.5 spaces by bedroom count, plus guest parking. The Zoning Administrator may approve a Minor Adjustment of up to 25 percent of a setback. See the parking, setbacks and height page.

Airport Zones, Specific Plans and Historic Resources

Ontario International Airport is inside the city, and Section 1.01.020 says that in a conflict with the Development Code "the requirements of the ALUCP shall govern." ALUCP is the airport land use compatibility plan. Its policy chapter says "New residential development is incompatible within all Safety Zones (1 through 5)," with exceptions for a house and a second unit on a legal lot in Zones 2, 3 and 4, and incompatible "within the projected CNEL 65 dB contour," with an exception for multi-family housing above 8 homes per acre. The City also lists 52 specific plans, and "the requirements of the Specific Plan shall govern" over the code. Work on a historic resource needs a Certificate of Appropriateness. See the airport zones and specific plans page.

Permits and Fees

The Planning Director, the City Engineer, the Zoning Administrator, the Planning Commission and the City Council each decide a set of applications. Ministerial permits must be decided within 60 days of a complete application. Hearing notices go to owners within 600 feet, and an appeal must be filed "within 10 days following the action or decision being appealed." A Development Plan lapses if not used within 24 months. The Planning fee schedule of August 22, 2026 lists Development Plan Review at $20,712.30 for less than 5 acres and a Tentative Parcel Map at $13,469.53. The development impact fee sheet effective July 1, 2026 totals $37,595 for a detached home, $29,674 for an attached home and $22,965 for a high density home, and the Ontario Ranch sheet totals $58,576, $42,405 and $31,026. See the permits and fees page.

How Current the Posted Code Is

The City puts the revision date in the name of each chapter file, and each page prints the date of the division it belongs to. The two can differ, because a file is reissued when any division in it changes.

Source: City of Ontario, Development Code page, files saved October 11, 2026. Chapter 8.0 (Sign Regulations) and References A to I were not read.

This guide read 47 City Council agendas to find the ordinances behind those dates and any that came later. These are the ones that change the Development Code or the Zoning Map.

Sources: City of Ontario, City Council agendas of February 4, 2025, April 1, 2025, August 19, 2025, November 4, 2025, December 16, 2025, February 17, 2026, March 3, 2026, July 7, 2026 and August 18, 2026; Council minutes of December 16, 2025 and August 18, 2026; Reference J.

Recent City Council Actions

• February 4 and 18, 2025. The agendas carried an urgency ordinance on ADUs, File No. PDCA24-004, "to comply with recent changes to state law" that took effect on January 1, 2025.
• March 18, 2025. The agenda carried public hearings on the regular ADU ordinance and on the Objective Development and Design Standards, and a resolution "ADOPTING THE DEVELOPMENT IMPACT FEE CALCULATION AND NEXUS UPDATE REPORT AND ADOPTING AN UPDATED AND MODIFIED DEVELOPMENT IMPACT FEE SCHEDULE." The fee resolution is No. 2025-010.
• April 1, 2025. The agenda listed both ordinances for adoption. Reference J records that the design standards were adopted that day by Ordinance No. 3298.
• August 19 and November 4, 2025. The agendas listed the adoption of two Development Code amendments, File No. PDCA25-001 and File No. PDCA25-002.
• December 16, 2025. The Council adopted Urgency Ordinance No. 3323 on ADUs by a 5-0 vote, according to the minutes.
• February 17 and March 3, 2026. The agendas listed the adoption of File No. PDCA25-003, which touched six chapters and the landscape guidelines, and File No. PDCA26-001 on temporary uses.
• June 23, 2026. The agenda carried a resolution on the Fiscal Year 2026-27 citywide fee schedule updates.
• July 7, 2026. The agenda listed the adoption of a citywide Zoning Map amendment, File No. PZC25-002, and of the Eucalyptus Business Park Specific Plan.
• August 18, 2026. The Council adopted Ordinance No. 3339, File No. PDCA26-002, on a consent calendar that the minutes say "carried by a vote of 5-0." The staff report lists nine changes, none of them to the ADU, SB 9 or residential standards sections.
• September 1 to October 6, 2026. The three agendas after August 18, the last of them for October 6, 2026, list no Development Code amendment.

Votes are stated only for December 16, 2025 and August 18, 2026, the two meetings whose minutes were read. The other items come from agendas, which show what was proposed.

Where the Code, City Documents and State Law Differ

The guide pages flag each difference where it arises. The main ones:

• The City's lot split section defines the eligible zone as LDR-5 only. Government Code 66411.7 speaks of a single-family residential zone, and AR-2, RE-2 and RE-4 also prohibit multiple-family dwellings.
• The City's SB 9 sections cap a new home at 800 square feet, and at 16 feet on a lot of 2,000 square feet or more. Government Code 65852.21, as amended, bars standards that do not apply uniformly within the zone, and LDR-5 allows houses of 35 feet.
• The two-unit section requires the owners to live on the lot and limits applicants to individuals. The statute lists the conditions a city may add, and neither one is on that list.
• Both SB 9 sections allow denial for an impact on the physical environment. The statutes name public health and safety.
• The ADU section exempts an ADU of less than 750 square feet from impact fees. Government Code 66311.5 exempts an ADU of 750 square feet or less.
• The City's ADU handout of January 2025 allows two detached ADUs on a multifamily lot. The code now allows up to 8.
• The Land Use Matrix prohibits alley-loaded and cluster houses in LDR-5. The standards tables print an LDR-5 column for both.
• Table 6.01-3 asks multiple-family buildings for 20 to 30 feet from a street. The 2025 design standards print 0 to 20 feet.
• The density bonus subsection describes one procedure that needs a Development Agreement and another that is ministerial.
• Section 6.01.020 still names mixed-use zones MU-2 and MU-11, which are absent from the list of zones in Section 5.01.005.
• The posted Chapter 6.0 ends the Affordable Housing Overlay text partway through, and has no standards section for the Chino Airport Overlay.

Limits of This Guide

The Development Code was read from the City's own PDFs, ten files in all. The Ontario Municipal Code as a whole is linked from the City Clerk page to an outside publisher whose site blocks scripted requests, so no request was sent there and the titles outside the Development Code were not read. That leaves out the building code, the noise chapter the code cites, the transient occupancy tax, and any rules on rental housing, tenants or mobile home rents outside the Development Code, and this guide makes no statement about them. City Council agendas were read from January 7, 2025 to October 6, 2026, with minutes for two meetings. Planning Commission agendas were not read. The Council may have acted on a housing rule after October 6, 2026.

These documents were not read: the Zoning Map and the interactive zoning map, The Ontario Plan and its Housing Element, the 52 specific plans, the 15 Planned Unit Development documents, the airport plan's policy maps, the Chino Airport plan, the Ontario Register of Historic Resources, the Building Department's permit fee tables, and the fee schedules of the school districts and utilities. Ask the Planning Department which standards and fees apply to your lot and whether a newer ordinance is in force.

Where to Go Next

Related on VanPlex: the California impact fees page, the San Bernardino guide and the Pomona guide.

Frequently Asked Questions

Official sources (checked October 2026)