Montgomery County, OH Accessory Structures: ADU Rules (2026)

Ohio counties do not adopt countywide zoning for unincorporated land. Under R.C. Chapter 519, zoning authority in unincorporated Ohio rests with townships, each of which adopts its own zoning resolution. The Montgomery County Planning Commission acts as the platting and subdivision authority for unincorporated Montgomery County and provides advisory recommendations on township zoning amendments, but it does not enforce a county zoning code. Whether an Accessory Dwelling Unit, in-law suite, or guest house is permitted - and whether it is allowed by right, by conditional use, or only by variance - depends on which township the property sits in (Butler, Clay, German, Harrison, Jackson, Jefferson, Miami, Perry, or Washington Township). In incorporated cities, R.C. Chapter 713 gives municipalities zoning authority and ADU rules vary city by city. Regardless of zoning, any one-, two-, or three-family dwelling - including a detached accessory structure used as habitable space - requires a building permit issued under the Residential Code of Ohio (OAC Chapter 4101:8). Montgomery County Building Regulations Division (937-225-4622) issues residential permits and conducts inspections. Owners must verify with both their township zoning inspector and Montgomery County Building Regulations before starting construction.