ADU Pass
Darke County
ADU Pass helps homeowners in Darke County, Ohio navigate the permit paperwork for building an accessory dwelling unit. We cover 14 cities and 17 ZIP codes in this county.
Map
County ADU details
County ADU ordinance
Darke County, Ohio (rural farming county on the Indiana border in western Ohio; ~51,881 residents per the 2020 census, ~51,520 estimated 2025; county seat Greenville; 20 townships - Adams, Allen, Brown, Butler, Franklin, Greenville, Harrison, Jackson, Liberty, Mississinawa, Monroe, Neave, Patterson, Richland, Twin, Van Buren, Wabash, Washington, Wayne, York; one city (Greenville) and 14 villages including Ansonia, Arcanum, Bradford, Burkettsville, Castine, Gettysburg, Gordon, Hollansburg, Ithaca, New Madison, New Weston, North Star, Osgood, Palestine, Pitsburg, Rossburg, Union City, Versailles, Wayne Lakes, and Yorkshire) is in the minority of Ohio counties that DOES exercise county-tier zoning powers under O.R.C. Chapter 303 - via a hybrid model. The Darke County Planning & Zoning Department (520 S. Broadway, Greenville; Zoning Inspector Kaitlin Higgins; 937-547-7381) directly administers township zoning resolutions for 9 of the 20 townships (Adams, Brown, Butler, Harrison, Jackson, Liberty, Neave, Wabash, Wayne) plus the Village of Wayne Lakes. Five townships (Franklin, Greenville, Monroe, Twin, Van Buren) administer their own township-tier zoning resolutions under O.R.C. Chapter 519, typically through a contracted zoning inspector. Six townships (Allen, Mississinawa, Patterson, Richland, Washington, York) remain unzoned, where the township trustees provide administrative approvals for building-site eligibility but no zoning permit is required. The county Planning & Zoning Department also serves as the countywide Floodplain Coordinator and administers the Darke County Subdivision Regulations for all unincorporated areas. Critically for ADU applicants: a Darke County Zoning Permit (issued by either the county Planning & Zoning Office or the self-administering township) must be in place BEFORE a state-side building permit is issued, regardless of which township the parcel sits in.
County assessor
Assessment policy: The Darke County Auditor (Carol Ginn as of 2026) is the elected property-assessment authority under O.R.C. § 5713.01. Ohio assesses real property at 35% of true value (O.R.C. § 5713.03). New ADU construction is added to the parcel record on the next regular revaluation cycle and assessed at true value as of January 1 following completion. Ohio law provides three significant ADU-relevant property-tax programs: (1) the Owner Occupancy Credit (O.R.C. § 323.151 et seq.) provides a 2.5% reduction in tax on owner-occupied homestead; (2) the Homestead Exemption (O.R.C. § 323.152) reduces taxable value by $25,000 for owners 65+ or totally and permanently disabled, subject to income tests; (3) Current Agricultural Use Valuation (CAUV) under O.R.C. § 5713.30 - § 5713.38 is very heavily used in Darke County, where agriculture is the dominant land use (Darke County consistently ranks in the top 5 Ohio counties for total crop and livestock value). An ADU built on a CAUV parcel may trigger a CAUV recoupment (3-year tax differential) under O.R.C. § 5713.34 if the new dwelling and its footprint reduce qualifying agricultural acreage below program thresholds, or if the ADU is found to be in non-agricultural use. Under O.R.C. § 5713.17, the owner must notify the Auditor of any construction or improvement valued over $2,000.
County overlays (4)
Known county issues (5)
- other — Researchers and ADU applicants must determine the parcel's township and zoning-administration channel BEFORE assuming any specific zoning rule. The Darke County Planning & Zoning Office (937-547-7381) is the correct first call regardless of township, and they will route inquiries to the township inspector if the parcel is in a self-administering township. Parcels in unzoned townships (Allen, Mississinawa, Patterson, Richland, Washington, York) carry materially more permissive ADU conditions than the rest of the county; parcels in the unincorporated areas of zoned townships face whatever the township resolution permits (single-family, two-family, accessory dwelling rules vary).
- other — ADU applicants should expect shorter plan-review turnaround than they would in a county served by DIC trip-routing, and inspector access is materially easier. Fee structures may differ from those quoted in any Ohio-wide guidance that assumes DIC fees. The county zoning permit must be issued before the county building permit will be released, regardless of which township the parcel is in.
- other — ADU economics in unincorporated Darke County are typically dominated by (a) septic / site-prep cost on poorly drained Stillwater / Greenville Creek bottom soils, (b) CAUV recoupment risk on agricultural parcels, and (c) livestock-operation proximity. Researchers should not assume the Adams County (Appalachian shale) cost band applies - Darke County's deep glacial till soils generally support conventional septic ($5,000-$12,000 range) on well-drained parcels, but poorly drained bottomland or high-water-table parcels may require mound or aerobic systems ($15,000-$35,000).
- policy-review — Researchers should monitor the Ohio General Assembly for any future ADU preemption proposal; until one passes, Darke County applicants must navigate the full hybrid zoning landscape described above. The 6 unzoned townships remain the most permissive ADU venues in the county, subject only to building code, septic capacity, and floodplain rules.
- other — ADU research aggregations should not assume county-recorded permit counts capture the full ADU production in Amish and Mennonite communities; un-permitted accessory dwellings are common in the New Weston / Burkettsville / Yorkshire concentration. Researchers projecting Darke County ADU activity from county permit data alone will undercount these communities materially.
Federal (United States) — ADU-relevant rules and programs
Federal ADU law
The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.
Federal financing programs
Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.
Federal tax credits
There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.
Federal housing programs
HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.