Allen County

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.

Process overview: For a township parcel: (1) confirm jurisdiction with LACRPC and the township zoning inspector (parcel in unincorporated Allen Co., specific township, applicable zoning district); (2) obtain a zoning certificate from the township zoning inspector against the adopted township zoning resolution — most Allen Co. township resolutions either omit ADUs entirely (which most interpret as not-permitted) or treat them as accessory uses subject to setback, lot-coverage, and maximum-accessory-structure-size limits; (3) submit a residential building permit application under OAC 4101:8 — for one- and two-family dwellings outside Lima, this is filed with the Ohio Department of Commerce / Division of Industrial Compliance (not Lima/Allen County Building Dept., which only does 1-3 family inside Lima); (4) obtain septic approval from Allen County Public Health if not on county sewer, or sewer-connection approval from Allen County Sanitary Engineering if county sewer is available; (5) obtain a floodplain development permit from LACRPC if the parcel intersects a mapped Special Flood Hazard Area (mandated by the Allen County Floodplain Management Regulations updated 2023); (6) construct with required inspections, then receive Certificate of Occupancy.

Impact fees: Allen County does not levy municipal-style residential impact fees on unincorporated parcels. Costs that DO apply: SmartGov portal fees ($50 per trade non-refundable for contractor registration), township zoning-certificate fee (varies by township; commonly $25-150), Ohio Division of Industrial Compliance residential plan-review fee (state schedule), Allen County Sanitary Engineering sewer-connection fee where applicable, Allen County Public Health septic-permit fee where applicable, and LACRPC floodplain-development-permit fee where the parcel is in a mapped SFHA.

The Allen County Auditor's Office (Rachael S. Gilroy, 301 N. Main Street, Lima, OH 45801, 419-223-8520) maintains parcel-level real-property assessment records countywide. An ADU addition is captured as an improvement to the host parcel through permit-data sharing from the Lima/Allen County Building Department (for Lima parcels) and from the Ohio Division of Industrial Compliance certificate-of-occupancy reporting (for non-Lima parcels). The Auditor's office operates Ohio's standard six-year reappraisal / three-year update cycle; the next Allen County triennial update is the year identified in the Department of Taxation's published Allen County cycle (verify at intake). Allen County offers CAUV (Current Agricultural Use Value) for qualifying farmland, the standard Ohio Homestead Exemption for qualifying senior/disabled owner-occupants, and accepts informal valuation reviews followed by formal Board of Revision complaints filed between the first Monday in January and March 31.

Assessment policy: An ADU added to a residential parcel increases the improvement value at the next reappraisal or triennial update. The Homestead Exemption (Ohio Revised Code 323.151-159) shields up to $25,000 of market value from taxation for qualifying senior or permanently-disabled owner-occupants of the principal residence; the exemption attaches to the parcel's principal residence, not the ADU, so adding an ADU does not eliminate Homestead, but the new ADU's improvement value is fully taxable. CAUV applies only to qualifying agricultural land and is generally incompatible with an ADU rented out as residential housing; consult the Auditor before adding an ADU to a CAUV parcel.

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.