ADU rules in Minnehaha County

In the unincorporated county, a detached ADU is allowed only as a conditional use in the A-1 Agricultural, RR Rural Residential, R-1 Residential and RC Recreation/Conservation districts, added by Ordinance MC16-183-25 (adopted by the County Commission 4-22-2025). It must sit on the same platted lot as the primary single-family dwelling, with only one ADU per parcel, on permanent frost-protective footings, with proof that the parcel can handle the added wastewater and no separate new access from a township, county or state road. ADUs are not listed in the Commercial or Industrial districts, and none may be placed in a regulated floodway.

An attached or internal ADU ('within or attached to an existing single family dwelling') is allowed on the same conditional-use basis as a detached one, in the A-1, RR, R-1 and RC districts only, subject to the same general requirements (one per parcel, wastewater capacity proven before the conditional use permit is approved, no separate access). It must meet all required setbacks and the county building code.

Article 12.20 caps a detached ADU at 50 percent of the primary dwelling's finished floor area and an attached ADU at 75 percent; there is no fixed square-foot ceiling. An existing single-family dwelling built more than 30 years ago may be adaptively reused as the ADU at up to 100 percent of the primary dwelling's size, provided wastewater requirements are met for both. A detached ADU in front of the main building takes the main building's setbacks; in the required rear yard it must be at least 7 feet from side and rear lines, and at least 10 feet from any other building.

Article 12.20 contains no owner-occupancy requirement for either the primary dwelling or the ADU, and South Dakota has no state ADU statute that would add or bar one. The Planning Commission can attach conditions to an individual conditional use permit under Article 19.05(C), so a specific approval could carry case-specific conditions.

Article 12.20(A)(6) requires two additional off-street parking spaces for the ADU, on top of the one space per dwelling unit that Article 15.02(A) requires for single-family dwellings.

Every ADU needs a conditional use permit decided by the Minnehaha County Planning Commission after a public hearing with mailed notice to owners within 500 feet and a posted sign, judged against the Article 19.05(D) criteria; the decision is final unless appealed to the Board of County Commissioners within five working days. After approval, a building permit from the Office of Planning and Zoning is required. The Commission has been granting ADU permits regularly since 2025 (for example CUP 26-10, 26-40 and 26-49 in 2026).

Article 12.20 does not restrict who lives in the ADU, and Article 12.19 states the ordinance does not intend to prohibit long-term lease or rental of lawful uses. A vacation home rental/short-term rental (a dwelling or portion rented daily or weekly for more than 14 days a year while not occupied by an owner or manager) is a separate conditional use in the A-1, RR, R-1 and RC districts under Article 12.17: maximum three people per bedroom, registration with the state as a Vacation Home, one parking space per guest bedroom, and owner and manager contact information filed with the Planning Department and posted inside. Separate sale of the ADU is effectively barred because it must stay on the same platted lot as the primary dwelling.