Milwaukee County, WI Accessory Structures: ADU Rules (2026)

Because every parcel of Milwaukee County land lies within an incorporated city or village, Wis. Stat. §59.69 (county zoning) does not apply - cities and villages exercise exclusive zoning authority under Wis. Stat. §62.23(7) and §61.35. The City of Milwaukee, which holds roughly 60 percent of the county's population, adopted a narrow 8-7 Common Council vote in 2025 amending Chapter 295 of the Code of Ordinances to permit ADUs as a Limited Use in residential single-family zones RS1, RS2, RS3, RS4, RS5, and RS6. Per the City's published ADU rules: only one ADU is allowed per property; the ADU must be smaller in gross livable area than the principal residence; the principal residence must be owner-occupied at the time of permit submission. Three configurations are allowed: Internal ADUs (inside an existing single-family home), Attached ADUs (added to a single-family home), and Detached ADUs (only allowed on lots with a single-family or 2-family principal residence). Permits and inspection are administered by the Department of Neighborhood Services through Milwaukee's Land Management System, with building-code review under Chapter 240. Surrounding municipalities - including Wauwatosa, West Allis, South Milwaukee, Cudahy, Greenfield, and the villages of Shorewood, Whitefish Bay, and Fox Point - each adopt their own ADU ordinances; check the relevant municipal code before designing. Wisconsin has no statewide ADU mandate.