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

Significant Restrictions

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

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

Key Facts

Size cap: 900 square feet
Permit required: Special Use Permit
Eligible districts: Agricultural, Rural Residential, Rural Suburban
Occupancy limit: 2 adults needing care
Rent: Prohibited

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 Missouri under recent ADU streamlining laws. The Cass County, MO rules below cover local size, height, and setback requirements.

Summary

Cass County allows a small accessory dwelling, what the Zoning Order calls a 'transitional living dwelling,' only by Special Use Permit on Agricultural, Rural Residential or Rural Suburban lots in unincorporated Cass County, capped at 900 square feet and restricted to caretaking arrangements for family members.

These county ordinances apply to unincorporated areas of Cass County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

Accessory structures may not be used as a dwelling, except that on a conforming lot which is zoned as Agricultural (A), Rural Residential (R-R) or Rural-Suburban (R-S) a single, transitional living dwelling no larger than nine hundred (900) square feet may be allowed by Special Use Permit.

View official code

Full Breakdown

' Outside those three districts, and without a Special Use Permit, converting an accessory structure into a second dwelling on the same lot is not allowed at all. ' The definition makes clear the unit is not a rental: 'Rent may not be charged for this facility,' it may not carry its own mailing address, and its housekeeping facilities are limited to a single bathroom and one kitchen. The Board of Zoning Adjustment sets the duration of the Special Use Permit, and the intent, per the definition, 'is to accommodate transitional living needs of family members, and not to provide for caretaking facilities' as a business. 030(A)(22).

Violations & Fines

Occupying an accessory structure as a dwelling without the required Special Use Permit, charging rent for a transitional living dwelling, or exceeding the 900-square-foot cap is a Zoning Order violation. The Zoning Enforcement Officer issues notice, the owner has ten days to correct it, and an uncorrected case is referred to Circuit Court where fines run up to $1,000 per day under Section 400.030(A)(22)(e).

Frequently Asked Questions

Can I build a garage apartment or accessory dwelling on my Cass County property?

Only as a 'transitional living dwelling' under Special Use Permit, and only on a conforming Agricultural, Rural Residential or Rural Suburban lot. It's capped at 900 square feet and limited to housing up to two adults who need care from the household in the principal home.

Can I rent out the accessory dwelling for income?

No. Section 400.050's definition is explicit that 'rent may not be charged for this facility,' because the unit is meant for family caretaking, not as a rental or investment property, and it cannot even carry its own separate mailing address.

What districts allow this kind of accessory dwelling?

Only three: Agricultural (A), Rural Residential (R-R) and Rural Suburban (R-S), under Section 400.030(A)(23). Platted residential districts like R-1 and R-2 are not listed, so a transitional living dwelling is not an option in those more urban zoning districts under the current Zoning Order.

Sources & Official References

[1]Cass County Code, Ch. 400 Zoning Regulations (eCode360)

Other rules in Cass County

Parking Rules: Street Parking LimitsSome Restrictions Noise Ordinances: Quiet HoursSome Restrictions Shed & Carport RulesSome Restrictions Parking Rules: RV & Boat ParkingLight Restrictions ADU Rental RestrictionsSignificant Restrictions Noise Ordinances: Decibel LimitsSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Parking Rules: Snow Removal Parking RulesSome Restrictions

All Cass County rules

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

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