Accessory Structures in Jefferson County, MO (2026)
2 rules for unincorporated Jefferson County, Missouri.
Verified from official government sources
ADU Rules
Jefferson County allows a permanent accessory dwelling unit, such as a mother-in-law cottage, in residential zoning districts with its own building permit, but it must meet the main house's setbacks, connect to approved water/sewer, and can never be sold apart from the primary home.
Jefferson County Accessory Dwelling Unit Standards
Some RestrictionsJefferson County UDO § 400.2770(B)
B. Standards For Accessory Dwelling Units. A dwelling unit may be allowed as an accessory use to the principal dwelling unit under the following conditions: 1. Accessory dwelling units may be constructed in a residential zoning district. This includes both planned and non-planned residential zoning districts and the "PM" Planned Mixed Use District. 2. An accessory dwelling unit may be construct...
Shed & Carport Rules
Jefferson County caps combined accessory-building square footage by district under UDO Section 400.2870: up to 4,000 square feet (or 5% of the yard) on RA-5 and LR-2 lots, 1,200 square feet on R-40 through R-7 lots. A shed of 200 square feet or less needs only a 15-foot rear setback.
Jefferson County Accessory Building Size Rules
Some RestrictionsJefferson County, MO UDO § 400.2870
In the "RA-5" Rural/Agricultural and "LR-2" Large Lot Residential Districts, there shall be permitted accessory buildings, combined square footage of which shall not exceed a total of four thousand (4,000) square feet or five percent (5%) of the lot area that is not occupied by the primary use, whichever is most permissive. Accessory buildings shall comply with Section 400.2770... In the "R-40"...
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