Spencerville

Allen County, Ohio (2023 population ~102,300; county seat Lima) is a non-charter county whose zoning authority over unincorporated land is exercised under O.R.C. Chapter 303 (county zoning) where adopted, and otherwise by individual townships under O.R.C. Chapter 519. As confirmed on the Lima/Allen County Regional Planning Commission (LACRPC) zoning page on 2026-05-20, the operative ADU-relevant zoning text for unincorporated Allen County land lives in township-level zoning resolutions, not a single countywide zoning resolution: Amanda Twp, American Twp, Auglaize Twp, Bath Twp, Jackson Twp, Marion Twp, Perry Twp, Richland Twp, Shawnee Twp, Spencer Twp, and Sugar Creek Twp each have adopted township zoning resolutions on file with LACRPC. Inside incorporated jurisdictions (City of Lima, Villages of Beaverdam, Bluffton, Cairo, Delphos, Elida, Harrod, Lafayette, Spencerville) zoning is set by the municipality under Ohio Constitution Article XVIII home rule. Allen County has not adopted a countywide accessory-dwelling-unit ordinance and no Ohio statewide ADU preemption is in force, so 'is an ADU permitted on this parcel?' depends entirely on which township or municipality the parcel sits in.

• Ohio Revised Code Chapter 303 (county rural zoning)
• Ohio Revised Code Chapter 519 (township zoning)
• Ohio Revised Code Sections 307.37 and 307.85 (Board of County Commissioners regulatory authority; floodplain regulation)
• Ohio Administrative Code 4101:8 (Residential Code of Ohio, one- two- and three-family dwellings)

State-floor overlay: Ohio has not enacted a statewide ADU preemption statute (see Ohio state-adu-research 2026-05-20). Allen County sits below the home-rule, township-and-municipal-controlled baseline; no statewide ADU floor preempts local rules.

Two countywide overlays meaningfully affect ADU project feasibility in Allen County. (1) FEMA-mapped Special Flood Hazard Areas covering 15,833.7 acres of Allen County (per LACRPC, 2026-05-20) trigger the Allen County Floodplain Management Regulations updated 2023, administered by LACRPC for unincorporated areas under delegation from the Board of County Commissioners' March 27, 2013 Flood Damage Reduction Resolution. (2) Comprehensive plans adopted by individual townships (Amanda, American, Auglaize, Bath, Perry, Richland, Shawnee, Sugar Creek) and municipalities (Lima Vision 2040, Bluffton Beyond Tomorrow, Cairo 2040, Elida, Harrod 2020-2040, Lafayette, Spencer-Spencerville) shape future-land-use designations that local zoning inspectors apply when reviewing accessory-dwelling proposals. There is no countywide historic-preservation overlay; historic-district review, where it exists, is municipal (Lima has a local landmarks designation process; villages generally do not).

• Allen County Floodplain Management Regulations (Unincorporated Areas), updated 2023 — FEMA floodplain maps are accessible through the Allen County Auditor's website. A new ADU sited in a mapped SFHA must meet the elevation-and-anchoring standard; project cost impact is typically material (often 10-25% of base ADU cost).
• Allen County Subdivision Regulations (administered by LACRPC for unincorporated areas) — LACRPC publishes a Land Division Process Brochure (2023) explaining the lot-split sequence.
• Allen County Sanitary Engineering sewer-service area — Main office: 3230 N. Cole St, Lima, OH 45801; (419) 996-4670.

Permitting for a residential ADU on an unincorporated Allen County parcel is split across three agencies: (1) the Lima/Allen County Building Department issues building permits and conducts commercial-code inspections countywide but, critically, enforces the Ohio Residential Code of Ohio (one-, two-, and three-family dwellings) ONLY within the City of Lima corporation limits — meaning a one- or two-family ADU on an unincorporated township parcel does NOT receive Lima/Allen County residential-code plan review and instead is enforced by the Ohio Department of Commerce, Division of Industrial Compliance, Bureau of Building Code Compliance, through the local Certified Residential Building Department or directly; (2) the township zoning inspector (or LACRPC where the township has delegated) issues the zoning certificate under the relevant township zoning resolution before any building permit can be released; (3) the Allen County Sanitary Engineering Department and the Allen County Public Health Department handle on-site septic / sewer approval, depending on whether the parcel is on a county sewer line (American, Auglaize, Bath, Jackson, Marion, Monroe, Perry, Richland, Shawnee, Sugar Creek Twps have county sewer infrastructure) or a private system.