Cass County, ND Accessory Structures: ADU Rules (2026)

Cass County does not have a single county-wide ADU ordinance. Township-level zoning ordinances (such as the Rich Township Zoning Ordinance amended March 2018) define principal and accessory structures, lot coverage, and setback requirements within each township's jurisdiction. Property owners outside city limits should contact the Cass County Planning Office and verify which township their parcel is in before adding an accessory dwelling. The Planning Office maintains township resources at casscountynd.gov/our-county/planning. Where no township zoning has been adopted, building safety requirements still apply and a development permit may be required from the County Planner. For parcels inside Fargo, West Fargo, Horace, Casselton, Mapleton, or other Cass County municipalities, the city zoning ordinance controls ADU rules - state preemption does not exist in North Dakota for ADUs. North Dakota has adopted the International Residential Code for residential construction, so any habitable accessory dwelling must meet IRC standards regardless of zoning.