ADU, Subdivision & Development in St. Louis County
Exploring an ADU, lot split, or development project? Get local zoning guidance for St. Louis County.
St. Louis County Planning Resources
St. Louis County Planning Department
Zoning, subdivisions, variances
41 S. Central Ave, Clayton, MO 63105
(314) 615-2500
Visit Website →St. Louis County Building Services
Permits and inspections (unincorporated)
41 S. Central Ave, Clayton, MO 63105
(314) 615-4145
Visit Website →Development in St. Louis County
90+ Municipalities = 90+ Rule Sets
St. Louis County is a patchwork of municipalities, each with different zoning codes, ADU rules, and subdivision requirements. Your first step is always determining whether you're in unincorporated St. Louis County or a specific city.
ADU/Accessory Dwelling
Rules vary by municipality. Some allow, some don't. Size limits, setbacks, and owner-occupancy requirements differ.
Subdivision/Lot Split
Contact Planning Department. Minimum lot sizes, frontage, and utility access vary by zoning district.
Variances
Need to deviate from zoning? Apply to Board of Adjustment. Requires demonstrating hardship.
Sell to Developer
Skip the hassle. Sell land with development potential to investors who handle entitlements.
Development too complicated? Sell your property with its development potential to an investor. Get your free property options report →
St. Louis County Development FAQs
Can I build an ADU in St. Louis County?
St. Louis County has 90+ municipalities, each with different rules. In unincorporated St. Louis County, ADUs may be allowed in certain residential zones with restrictions. Many municipalities like Clayton, Webster Groves, and Kirkwood have their own ADU regulations. Contact your specific city's planning department or St. Louis County Planning for unincorporated areas.
How do I subdivide property in St. Louis County?
For unincorporated St. Louis County, contact the Planning Department at (314) 615-2500. You'll need a survey, application, and review for compliance with minimum lot sizes, frontage, and utilities. For incorporated areas, contact your city's planning department. Process takes 3-12 months depending on complexity.
What are the minimum lot sizes in St. Louis County?
Lot sizes vary dramatically by zoning district. R-1 zones may require 15,000+ sq ft; R-4 zones might allow 6,000 sq ft. Each municipality sets its own requirements. Check your specific zoning district requirements before planning a subdivision.
Do I need to work with the county or my city?
If you're in unincorporated St. Louis County, work with County Planning and Building Services. If you're in an incorporated city (like Kirkwood, Webster Groves, Ballwin), work with that city's planning and building departments. Not sure? Check your property tax bill or the County GIS system.
Should I subdivide myself or sell to a developer?
Subdividing yourself maximizes profit but requires time (6-12+ months), capital for surveys and fees, and navigation of approval processes. Selling to a developer is faster but yields less. Consider getting preliminary subdivision feasibility reviewed before deciding.
Documents for St. Louis County Development Projects
Having these items ready helps us give you accurate guidance faster:
- Property deed
- Current survey/plat
- Property tax records (shows jurisdiction)
- Zoning classification
- Title report
- Utility locations
- HOA rules (if applicable)
- Previous permits
Don’t have everything? That’s okay – start with what you have.
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Free consultation on ADUs, subdivisions, or selling land with potential.
Important: This information is educational and specific to St. Louis County, Missouri. Zoning and development regulations vary by municipality. Always verify requirements with the appropriate planning department.