Freeport

Harrison County's principal overlays affecting ADU feasibility are: (1) FEMA NFIP Special Flood Hazard Areas — Harrison County participates in the National Flood Insurance Program; the dominant flood-source watersheds are Stillwater Creek (a Tuscarawas River tributary, headwatered in Harrison County), Short Creek (an Ohio River tributary), Conotton Creek (shared with Carroll and Tuscarawas counties), and the shorelines of Tappan Lake (Stillwater Creek impoundment) and Clendening Lake — both USACE-built reservoirs in the Muskingum Watershed Conservancy District (MWCD); (2) MWCD shoreline / encroachment overlay — Tappan Lake, Clendening Lake, and the smaller Piedmont Lake (Belmont/Harrison) are all MWCD reservoirs, and parcels with lake frontage or within MWCD easements require MWCD encroachment permits for any new structure, dock, or shoreline modification (this overlay regularly blocks or delays ADUs on shoreline parcels); (3) Mandatory coal-mine-subsidence insurance overlay — Harrison County is one of the 26 Ohio counties listed under O.R.C. § 3929.51 et seq. as mandatory-coverage counties for mine-subsidence insurance through the Ohio Mine Subsidence Insurance Underwriting Association (OMSIUA); homeowner policies in Harrison County automatically carry the mine-subsidence rider, and any ADU added to a covered parcel inherits the rider but structure-specific underwriting should be confirmed; (4) Surface and underground coal-mining activity — Harrison County remains one of Ohio's most active surface-mining counties (Pittsburgh and other Allegheny-formation seams under permit by ODNR Division of Mineral Resources Management), and abandoned-mine-land subsidence risk in mapped undermined areas is a real constraint on foundation design; (5) Utica Shale oil-and-gas overlay — Harrison County has been the single most heavily drilled Utica Shale county in Ohio by total well count since 2011, with horizontal-well pad permits administered by ODNR Division of Oil and Gas Resources Management under O.R.C. Chapter 1509 (preempting local zoning per State v. Munroe Falls, 2015); surface easements for producing wells, pads, gathering lines, and compressor stations materially constrain where an accessory structure can be sited; (6) No county historic-district overlay — Harrison County does not operate a county historic-preservation commission, though individually-listed National Register properties exist in Cadiz (Edwin M. Stanton birthplace site and the Cadiz Historic District) and elsewhere.

• FEMA NFIP Special Flood Hazard Areas in Harrison County (Stillwater Creek, Short Creek, Conotton Creek, Tappan Lake, Clendening Lake, Piedmont Lake shorelines) — Stillwater Creek and its tributaries account for most fluvial flood exposure in Harrison County. MWCD reservoir releases from Tappan and Clendening alter downstream Stillwater Creek hydrology and have produced documented downstream flooding in wet years.
• Muskingum Watershed Conservancy District (MWCD) shoreline / encroachment overlay — Tappan Lake, Clendening Lake, Piedmont Lake — MWCD does not preempt township zoning but adds an additional consent layer. MWCD has historically been conservative about new shoreline residential construction and frequently denies or conditions encroachment requests for accessory dwellings on reservoir frontage.
• Mandatory coal-mine-subsidence insurance (Pittsburgh and Allegheny-formation seams; historic and active mining) — Harrison County retains active surface-mining operations under ODNR permit; review proximity to any active permit boundary before siting an ADU, because blasting, haul-road, and reclamation activity can affect both habitability and insurability.
• Utica Shale horizontal-well pad surface-use overlay (heaviest-drilled Utica county in Ohio) — Confirm any oil-and-gas surface easement, road-use agreement, and pad-set-aside acreage at title search before committing to an ADU site plan. This overlay does not require a county permit but can be the single largest siting constraint on a Harrison County parcel.
• Cadiz Historic District (Village of Cadiz, NRHP-listed) and Edwin M. Stanton birthplace site — Outside Cadiz, individually-listed NRHP properties exist in Harrison County (e.g. courthouse-square structures) but there is no county-level historic-district overlay.