Ontario — Historic Preservation

Last reviewed: July 3, 2026

Overview

This page explains how Ontario's Development Code handles local historic resources: how properties are identified and listed on the Ontario Register, how designations (Local Historic Landmarks, Local Historic Districts, and Architectural Conservation Areas) are made, what triggers review, and what incentives or limitations apply. It is strictly limited to rules in the City of Ontario's Development Code (Title references below) and points you to the specific review rules you will face if your property is on or near the Ontario Register. For zoning context see Ontario Zoning and Ontario Land Use; for standards and departures see Ontario Development Standards and Ontario Overlay Districts.

Core rules and processes (plain-English, code-grounded)

• A local register called the Ontario Register of Historic Resources exists and the Historic Preservation Subcommittee maintains eligibility and listings § 7.01.010 .
• Formal local designations (Local Historic Landmark, Local Historic District, Architectural Conservation Area) use the findings and criteria in § 4.02.040 ; nominations are processed per the review matrix in Table 2.02-1 and subject to hearings § 4.02.040 and Table 2.02-1 .
• A Certificate of Appropriateness (COA) (or waiver) is required before permits for exterior alteration, demolition, relocation, infill, or exterior work on historic resources or noncontributing resources inside a district are issued § 4.02.050 .
• The Code uses a three-tier ranking (Tier I / Tier II / Tier III) to determine the level of environmental review and how strongly demolition is discouraged; the tier definitions and criteria are in § 4.02.040.G and related subsections § 4.02.040 .
• The City offers targeted incentives (e.g., California Historical Building Code use, parking reductions, setback/height adjustments, fee waivers, grant/loan programs, and Mills Act facilitation) for eligible preservation projects; see § 7.01.015 and § 7.01.025 .
• If a property is proposed for demolition, mitigation fees may be required and are established under § 7.01.030; fees (10–30% of sq ft valuation) fund preservation efforts unless reduced to avoid a taking § 7.01.030 .
• Adaptive reuse of qualifying historic buildings is a ministerial pathway with flexibility on development standards (parking, height, FAR, open space) and alternative building/fire code compliance; see § 4.03.010 .

District-by-district breakdown

Note: Historic preservation provisions apply citywide where properties are on the Ontario Register or lie within a designated, eligible, or potential historic district; below are districts and overlays that the Code specifically ties to historic preservation.

EA (Euclid Avenue) Overlay

• Purpose: Recognize and protect Euclid Avenue as a scenic and historic resource and to safeguard its status on the National Register of Historic Places § 6.01 (EA Overlay) .
• Typical permitted uses: Uses follow the underlying base zoning; the overlay does not create new land uses but applies special development and review rules (e.g., Downtown Ontario Design Guidelines) § 6.01 (EA Overlay) .
• Key standards / triggers:
  • Projects requiring Development Plan approval in the EA Overlay must obtain a Certificate of Appropriateness § 6.01 (EA Overlay) and § 4.02.050 .
  • Euclid-fronting lots are required to locate parking to the side or rear and ground-floor use restrictions apply in some MU-1 areas (see MU-1) § 6.01 (EA Overlay) and related development standards .
• Where it applies: Mapped overlay along Euclid Avenue downtown as shown on the Official Zoning Map and documented in the overlay text § 6.01 .

MU-1 (Downtown Mixed Use)

• Purpose: Focus downtown regeneration and protect/enhance the historic character of Ontario's historic downtown; MU-1 is explicitly designed to "recognize, protect, and enhance" the historic downtown and Euclid/Holt corridors § 5.01.0 (MU-1) .
• Typical permitted uses: Intensive mixed uses—retail, entertainment, restaurants, galleries, work/live, residences at 25–75 DU/AC, and FAR up to 2.0 in core areas § 5.01.0 (MU-1) .
• Key dimensional/operational points:
  • MU-1 is divided into LUA areas (Euclid Avenue Entertainment, Arts, Holt Blvd, Civic Center) with block-level use restrictions and a Euclid protection corridor for ground-floor uses § 5.01.0 .
  • Projects in MU-1 that are within the EA overlay or the Ontario Register are subject to Certificate of Appropriateness requirements § 4.02.050 and to Downtown Ontario Design Guidelines referenced in the MU-1 text .
• Where it applies: Downtown core—refer to Figure 5.01-1 and Figure 5.01-2 in the Code § 5.01 .

MU-3 (East Guasti Mixed Use)

• Purpose: Encourage development that "respects the history of the adjacent Guasti Winery" and retains important historic resources such as San Secondo d'Asti Church § 5.01 (MU-3) .
• Typical permitted uses: Low-rise offices, retail, lodging, and residential (20–65 DU/AC; 1.0 FAR commercial) § 5.01 (MU-3) .
• Key standards:
  • Because the MU-3 area includes known historic resources, preservation rules in Division 7.01 and designation/COA rules in § 4.02.040 and § 4.02.050 apply when a resource is listed or eligible .
• Where it applies: East Guasti area, per the MU-3 map and text § 5.01 .

Architectural Conservation Areas (designation, not a zoning district)

• Purpose: To protect areas that have architectural cohesiveness but which may not meet historic-significance criteria; these do not themselves qualify properties for landmark status but may impose design guidance § 4.02.040.I .
• Typical effect: Properties in Architectural Conservation Areas are subject to conservation plans and design guidelines; COAs and design review may still apply depending on the conservation plan § 4.02.040.I .

Quick reference table — decision‑relevant items

Practical guidance / interpretation (how this plays out)

• If your property is on the Ontario Register or within an eligible/ designated historic district, factor a COA and likely public hearing into any exterior work timeline — § 4.02.050 .
• Expect the Historic Preservation Subcommittee to do a "determination of significance" using National/California Register criteria and possibly require an intensive Historic Resource Survey prepared to OHP standards before designation or COA hearings § 4.02.050.C and § 7.01.010.C .
• The Code provides incentives to make preservation viable: ask about CHBC use, parking relief, and setbacks/height relief early — these are authorized at staff or Commission level in § 7.01.025 and § 7.01.015 .
• For adaptive reuse projects, the Adaptive Reuse Plan path can relax parking, FAR, height, and allow alternative fire/building code compliance — see § 4.03.010 .
• ADU permit applicants: ADU parking exceptions exist if the lot is within an "architecturally and historically significant historic district" (so ADU parking rules may be relaxed) — see ADU rules § 5.03 (ADU parking exceptions) .

(Other development rules—parking, setbacks, signs—still apply; see Ontario Parking, Ontario Development Standards, Ontario Signage for interactions with preservation rules.)

• parking → Ontario Parking
• development standards → Ontario Development Standards
• design review → Ontario Design Review
• overlay districts → Ontario Overlay Districts
• ADUs → Ontario ADUs
• Title 24 / CHBC context → California Building Standards Code
• zoning overview → Ontario Zoning
• land use plan context → Ontario Land Use

Checklist

• Confirm whether the property is on the Ontario Register or an eligible/potential district (§ 7.01.010) .
• If designated or eligible, prepare to file a Historic Preservation—Certificate of Appropriateness or request a waiver (§ 4.02.050) .
• If COA required, commission a Historic Resource Survey at the appropriate level (reconnaissance or intensive) per California OHP standards § 4.02.050 and § 7.01.010.C .
• Expect environmental review tied to the Tiering (Tier I/II requires EIR; Tier III may require an EIR addendum) § 4.02.050.C.2 and § 4.02.040.G .
• Consult the Historic Preservation Subcommittee/Historic Preservation Commission early to identify possible incentives (CHBC, parking relief, setback/height adjustments, grants/Mills Act) § 7.01.015–7.01.025 .
• If demolition is proposed, budget for the Historic Preservation Mitigation Fee and possible public review § 7.01.030 .
• If seeking adaptive reuse of a qualifying building, prepare an Adaptive Reuse Plan that includes building-condition reports and architectural qualifications § 4.03.010 .
• Verify overlay status (EA, AG, ICC, MTC, etc.) as overlays can impose additional COA or design-review triggers § 6.01 (Overlay Districts) .

Risks & Ambiguities

Plain-English Summary

If your Ontario property is listed on the Ontario Register or inside a designated historic area, you will likely need a Certificate of Appropriateness before doing exterior work or demolition, and the City may require historic surveys and environmental review; in return the City offers targeted incentives (parking relief, setback/height adjustments, CHBC use, grants) to make preservation feasible § 4.02.050, § 7.01.025, § 4.03.010 .

Source References

• § 4.02.040 Historic Preservation—Local Historic Landmark and Local District Designations, Historic Resource Tiering, and Architectural Conservation Areas
• § 4.02.050 Historic Preservation—Certificates of Appropriateness and Demolition of Historic Resources (COA triggers, processing, inspections)
• § 4.02.045 Rescind or Amend Status of a Historic Resource (removal/rescission process)
• § 7.01.000 – 7.01.045 Division 7.01 Historic Preservation (Ontario Register, incentives, CHBC, mitigation fee, Trust Fund) — see especially § 7.01.010, § 7.01.015, § 7.01.025, § 7.01.030
• § 4.03.010 Adaptive Reuse Plan (ministerial pathway, standards relief)
• Historic Preservation Commission and Subcommittee powers and duties § 2.01.020 and § 2.01.025
• EA (Euclid Avenue) Overlay provisions (COA trigger and design guidelines) — Division 6.01 (EA Overlay)
• MU-1 (Downtown Mixed Use) district purpose and land‑use areas (Euclid/Holt) — § 5.01 (MU-1)
• ADU parking exception for historic districts — Division 5.03 (ADU provisions)

Retrieved passages

• Ontario Zoning Code (Section 4.02.040) High relevance show source text
• Ontario Zoning Code (Section is) High relevance show source text
• Ontario Zoning Code (Section is) High relevance show source text
• Ontario Zoning Code (Section 4.02.040) High relevance show source text
• Ontario Zoning Code (Title 1) High relevance show source text
• Ontario Zoning Code (Section 2.02.015.B) High relevance show source text
• Ontario Zoning Code (Section is) High relevance show source text
• Ontario Zoning Code (Section 2.02.015.B) High relevance show source text
• Ontario Zoning Code (Section 4.02.025) High relevance show source text
• Ontario Zoning Code (Section 4.02.025) High relevance show source text
• Ontario Zoning Code (Title 4) Medium relevance show source text
• Ontario Zoning Code (Section 6.02.020) Medium relevance show source text
• Ontario Zoning Code (Section 6.02.025) Medium relevance show source text
• Ontario Zoning Code (Title 4) Medium relevance show source text
• Ontario Zoning Code (Section 6.01.010.H) Medium relevance show source text
• Ontario Zoning Code Medium relevance show source text
• CBC § 7.01.030 (Section 7.01.030) Medium relevance show source text
• Ontario Zoning Code (Title 4) Medium relevance show source text
• Ontario Zoning Code (Section 1.02.010) Medium relevance show source text
• Ontario Zoning Code (Section 65583.) Medium relevance show source text
• Ontario Zoning Code (Section 65583.) Medium relevance show source text

Cited sections

• **§ 4.02.040** Historic Preservation—Local Historic Landmark and Local District Designations, Historic Resource Tiering, and Architectural Conservation Areas (§ 4.02.040)
• **§ 4.02.050** Historic Preservation—Certificates of Appropriateness and Demolition of Historic Resources (COA triggers, processing, inspections) (§ 4.02.050)
• **§ 4.02.045** Rescind or Amend Status of a Historic Resource (removal/rescission process) (§ 4.02.045)
• **§ 7.01.000 – 7.01.045** Division 7.01 Historic Preservation (Ontario Register, incentives, CHBC, mitigation fee, Trust Fund) — see especially **§ 7.01.010**, **§ 7.01.015**, **§ 7.01.025**, **§ 7.01.030** (§ 7.01.000)
• **§ 4.03.010** Adaptive Reuse Plan (ministerial pathway, standards relief) (§ 4.03.010)
• Historic Preservation Commission and Subcommittee powers and duties **§ 2.01.020** and **§ 2.01.025** (§ 2.01.020)
• EA (Euclid Avenue) Overlay provisions (COA trigger and design guidelines) — Division 6.01 (EA Overlay)
• MU-1 (Downtown Mixed Use) district purpose and land‑use areas (Euclid/Holt) — **§ 5.01 (MU-1)** (§ 5.01)
• ADU parking exception for historic districts — Division 5.03 (ADU provisions)
• Ontario_ZoningCode.md

• Official Ontario code library