1 county-level rule, plus city-specific rules for 2 cities in St. Louis County, Missouri.
Verified from official government sources
Missouri has no statewide ADU mandate. St. Louis County's Zoning Ordinance (SLCRO 1003) regulates accessory buildings in unincorporated areas, but does not include a dedicated detached ADU permission for most residential zone districts. Detached above-ground accessory structures are capped at seven percent of the lot area, limited to one detached garage plus two additional accessory structures, and may not exceed the height of the primary dwelling or be placed in the front yard. Each of the 88 incorporated municipalities in St. Louis County (Florissant, Kirkwood, Ferguson, etc.) may have separate ADU rules.
2 cities in St. Louis County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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