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

Heavy Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Marathon County, WI, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Detached accessory dwelling use: Prohibited
Max dwelling units per residential lot: One (or two-family)
Applies only in: Towns adopting county zoning

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Wisconsin under recent ADU streamlining laws. The Marathon County, WI rules below cover local size, height, and setback requirements.

Summary

Marathon County zoning flatly bars using a detached garage, shed, or other accessory building as a separate dwelling unit, and residential lots are capped at one house anyway.

City-specific rules exist: Wausau has its own adu rules rules that differ from Marathon County's county-level regulations. If you live in Wausau, check the city-specific page instead.

Detached Accessory Buildings. Detached accessory buildings shall not be used as a separate dwelling unit and shall comply with the requirements of the following Table 6.C.Accessory Structures Housing Livestock. Section 17.204.01.A.3.D.Accessory Structures within shoreland jurisdiction. Existing and new accessory buildings shall comply with all Marathon County shoreland regulations and provisions. Table 6: DETACHED ACCESSORY BUILDING STANDARDS Requirement Residential Districts (U-R) Residential Districts (L-D-R and RR) Residential District (RE) Agricultural Districts (GA and FP) Any Other Zoning District Location Rear, side or front yard Rear, side or front yard Rear, side or front yard Rear, side or front yard Rear, side or front yard Setback Requirements from principal structure 15 feet 15 feet 15 feet 15 feet 15 feet from side property line 7 feet 7 feet 7 feet 7 feet Minimum setback required in zoning district from rear property line 7 feet 7 feet 7 feet 7 feet Minimum setback required in zoning district Maximum side wall height 16 feet None None None None Maximum Size 1,400 sq.ft. 2,000 sq.ft. NONE NONE NONE Maximum Height (**) 24 feet 24 feet 35 feet ** 35 feet ** 35 feet **
* In Shoreland areas: Refer to Chapter 22 Marathon County Shoreland, Shoreland-Wetland, and Floodplain Regulations. ** For height exemptions refer to Section 17.202.07.

View official code

Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 59).

Full Breakdown

The zoning code states plainly that a detached accessory building cannot be converted into or used as a separate dwelling unit: it must stay accessory to the house on the lot. That backstops a broader rule limiting residential lots to no more than one single-family or two-family dwelling unit, so a second, independent living unit in a garage or outbuilding isn't an option under county zoning. This applies only in towns where the town board has adopted the county's general zoning ordinance; it has no effect inside Wausau or any incorporated city or village, and towns that opted out set their own rules.

Violations & Fines

Building or occupying a detached accessory structure as a dwelling unit is a zoning violation subject to a forfeiture under Chapter 25.04 plus prosecution costs, with each day of continued violation counted separately (§ 17.807).

Frequently Asked Questions

Can I turn my garage into a rental unit in Marathon County?

No. County zoning specifically says a detached accessory building shall not be used as a separate dwelling unit.

Does this rule apply inside Wausau?

No. Wausau has its own city zoning code; the county's accessory-structure rule only governs unincorporated towns that adopted county zoning.

Sources & Official References

[1]Marathon County Code of Ordinances (Municode)

Other rules in Marathon County

Parking Rules: Street Parking LimitsSome Restrictions Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions Noise Ordinances: Vehicle NoiseSome Restrictions Noise Ordinances: Amplified Music & Outdoor SoundSignificant Restrictions Noise Ordinances: Barking DogsSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions

All Marathon County rules

How Marathon County compares: Easiest Cities to Build an ADU·Compare Marathon County to another location·View the Wisconsin accessory structures overview

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ADU Rules in Cities Across Marathon County

Rothschild, WI Wausau, WI