Hammondsville

Jefferson County is located in eastern Ohio along the Ohio River, directly across from Weirton and Wheeling, West Virginia, with the county seat at Steubenville. The county covers about 411 square miles, contains 14 townships and 19 incorporated municipalities (2 cities, 17 villages), and had a 2020 population of about 65,249. Ohio operates under a strong home-rule framework (Ohio Const. Art. XVIII, Sec. 3), and the state has not enacted any ADU preemption or by-right ADU statute. Authority over ADU zoning and permitting in Jefferson County is split between (a) the county itself, which may adopt countywide zoning under O.R.C. Chapter 303 but has not done so, (b) the county's 14 townships in the unincorporated balance, which may adopt township zoning under O.R.C. Chapter 519, and (c) each incorporated municipality (city or village) under its home-rule zoning power. Practically, ADU rules in Jefferson County are set by the specific township or municipality, not by the county. The Jefferson County Regional Planning Commission (JCRPC) reviews subdivision plats and provides advisory planning services but does not exercise zoning authority over individual parcels.

• Ohio Const. Art. XVIII, Sec. 3 (Home Rule)
• O.R.C. Chapter 303 — County Rural Zoning
• O.R.C. Chapter 519 — Township Zoning
• O.R.C. Chapter 713.21-.27 — Regional Planning Commissions

State-floor overlay: No Ohio statewide ADU preemption is in force as of 2026-05-20. The Residential Code of Ohio (RCO, OBBS-adopted IRC with Ohio amendments) sets the building-code floor for one- and two-family dwellings statewide, but use, density, setbacks, parking, and owner-occupancy are local. The county itself retains no zoning authority because Jefferson County has not adopted Chapter 303 rural zoning.

Jefferson County's principal county-administered overlays affecting ADU feasibility are (a) FEMA NFIP Special Flood Hazard Areas along the Ohio River and its tributaries (Yellow Creek, Cross Creek, Wells Creek, McIntyre Creek, Short Creek), administered through the county's NFIP-participating floodplain ordinance for the unincorporated areas, (b) the legacy of deep-mine coal extraction (Pittsburgh No. 8 seam) across the county, which expresses as subsidence-prone undermined ground, and (c) very active Utica/Marcellus shale oil-and-gas development, which expresses as parcel-level unitization, well-pad surface easements, and gathering-line infrastructure. Jefferson County is described by its own Port Authority as 'in the bulls-eye' of the Marcellus/Utica play; the density of recent unconventional well permits and pads is among the highest in Ohio. The county itself does not maintain a historic-district overlay; municipal historic districts exist (notably parts of downtown Steubenville's Fort Steuben / Market Street area and parts of Toronto). Wildland-urban-interface fire mapping is not maintained as a binding overlay in Ohio at the county level.

• Jefferson County Floodplain Management (FEMA NFIP participation) — A new ADU in a Zone AE Ohio River SFHA parcel must be elevated to or above the Base Flood Elevation per the applicable floodplain ordinance and 44 CFR 60.3. Substantial-improvement triggers apply when an ADU project's cost exceeds 50 percent of the host structure's pre-improvement market value.
• Coal-mine subsidence risk (Pittsburgh No. 8 seam undermining) — Subsidence is not a zoning overlay in the regulatory sense — the county does not block construction — but it is a material constructability and insurance consideration that distinguishes ADU work in Jefferson County from ADU work in non-mining Ohio counties.
• Utica / Marcellus shale unitization, well pads, and gathering infrastructure — This is a parcel-level title and surface-easement issue rather than a zoning overlay; it is included here because it is one of the most common Jefferson-specific factors that derails an otherwise-allowed ADU.
• Steubenville and Toronto Community Reinvestment Areas (CRAs) and Enterprise Zones — Confirm the parcel is inside the specific CRA target area at the City of Steubenville Department of Community and Economic Development or the City of Toronto before relying on the abatement in project pro formas.

Jefferson County does not operate a county-administered residential building inspection program. Ohio's Residential Code of Ohio (RCO) applies statewide to one- and two-family dwellings, but local enforcement is opt-in: the State of Ohio Board of Building Standards (BBS) certifies local building departments to enforce the RCO, and where no certified local department exists, residential plan review and inspection for RCO compliance are not actively enforced on a parcel-by-parcel basis for one- and two-family dwellings. Jefferson County itself is not a BBS-certified residential building department; residential ADU work in unincorporated, unzoned townships proceeds through Jefferson County General Health District on-site sewage and water review, the Jefferson County Engineer for driveway/right-of-way access, county floodplain review (if within an SFHA), 911 addressing, and any applicable township zoning, but without a county-level building permit. Commercial and multi-family work in unincorporated areas defaults to the State of Ohio Department of Commerce, Division of Industrial Compliance. Inside incorporated municipalities, the city or village handles its own permits.