St. Mary's County's Department of Land Use and Growth Management at 23150 Leonard Hall Drive in Leonardtown processes building permits alongside environmental, residential entrance, home occupation, family daycare, change of business occupant and sign permits, and routes each to the other agencies that must review it. On a peninsula county with this much shoreline, its Critical Area rules do more work than its building code: any development activity in the Critical Area — disturbance to land, to natural vegetation, or a structural addition or placement — requires authorisation, and the application carries a Critical Area quality site plan.
Two thresholds follow from that. A project proposing to disturb more than 5,000 square feet typically needs an erosion and sediment control plan and a stormwater management plan designed by a professional surveyor or engineer; and disturbance to the Critical Area Buffer routinely requires variance approval from the Board of Appeals — a hearing, not a counter transaction. The department's offices are open through the working day but permit applications are accepted only in shorter windows, longer on Tuesdays, Wednesdays and Fridays than on Mondays and Thursdays.
This guide covers St. Mary's County, including Lexington Park, California, Great Mills and Mechanicsville, all unincorporated. The Town of Leonardtown has its own municipal role; confirm the town's approvals as well as the county's before filing inside it.
In the Critical Area, clearing is development. The county treats any development activity — disturbance to land, to natural vegetation, or structural additions and placement — in the Critical Area as requiring authorisation, with a Critical Area quality site plan attached to the application. Clearing brush before the survey is done is itself the regulated act, and disturbance to the Buffer routinely requires a variance from the Board of Appeals.
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Get a free quote →What requires a building permit in St. Mary's County?
Typically permit required
- Any development activity in the Chesapeake Bay Critical Area, including clearing vegetation, with a Critical Area quality site plan
- Disturbance over 5,000 square feet, which needs erosion and sediment control and stormwater management plans by a surveyor or engineer
- Residential entrances, home occupations, family daycare, changes of business occupant and signs, each permitted by the same division
- New buildings, additions and any structural work on an existing building
- Interior alterations that reconfigure space, add plumbing fixtures or extend circuits, under the building or residential code and the Maryland Building Rehabilitation Code
- Decks, accessory structures above the local exemption threshold, retaining walls and swimming pools, including above-ground pools
Often exempt
- Work outside the Critical Area that the adopted codes place below the permit threshold; the department's customer assistance guides set out the cases
- Painting, wallpapering, interior finishes, cabinets, flooring and trim
- Like-for-like replacement of windows and doors in the same opening
- Small detached accessory structures below the jurisdiction's exemption threshold and fences below its height limit — the zoning rules still apply
- Minor repairs that do not remove or alter structural members
What is actually local, and what is not
The code editions are the state's. St. Mary's County's layer is the enforcing office and its amendments to the building and residential codes, its fee schedule, its grading ordinance and its stormwater programme under MDE criteria, and the Critical Area authorisation and Buffer variance that the department administers ahead of the building permit.
Maryland enforces one statewide set of codes, the Maryland Building Performance Standards (COMAR 09.12.51), through the county or city permit office, which may amend the building and residential codes for local conditions. Maryland rules
Who handles permitting in St. Mary's County?
The Department of Land Use and Growth Management is the enforcing office, with its Permit Services Division processing and routing applications and its inspections division carrying the field work; the Board of Appeals, Planning Commission and Technical Evaluation Committee all sit under the same department. The Metropolitan Commission handles public water and sewer, and the department publishes customer assistance guides answering the recurring permit questions.
| Detail | Information |
|---|---|
| Department | St. Mary's County Department of Land Use and Growth Management |
| Office | 23150 Leonard Hall Drive, Leonardtown, MD 20650 |
| Phone | (301) 475-4200, extension 1500 |
| Office hours | Monday to Friday, 8:00 am to 5:00 pm; appointments recommended |
| Permit counter | Monday and Thursday 8:30 am to 2:00 pm; Tuesday, Wednesday and Friday 8:30 am to 4:30 pm |
| Critical Area | Authorisation with a Critical Area quality site plan for any development activity |
Not sure this scope needs a permit?
Get a free quote →In 2025, building permits issued in unincorporated St. Marys County authorized 236 new privately owned housing units, all of them single-family homes, according to the U.S. Census Bureau Building Permits Survey.
Permit types
Residential permits
A St. Mary's house project files with the Critical Area, floodplain, airport overlay and noise zone questions answered on the application itself, three prints of floor plans with each room's use labelled, and digital submittals emailed to the department's building permit service address. Where the property is not in a recorded subdivision, recorded deeds dating back to March 1978 are filed with it; where the applicant is not the owner, a contract of sale, lease or notarised permission comes too. An addition to a house on septic states the size of the existing dwelling the system serves.
Commercial permits
Commercial work in St. Mary's clears zoning and the Technical Evaluation Committee, then building plan review, with the Critical Area and stormwater plans prepared by a surveyor or engineer where the disturbance thresholds are crossed. The Lexington Park and Patuxent River Naval Air Station corridor carries airport overlay and noise zone questions that the application asks about directly.
Prior approvals, plan review and the local clock
In St. Mary's County the Chesapeake Bay Critical Area and its Buffer govern the shoreline, the airport overlay and noise zones govern the land around Patuxent River Naval Air Station, and the soil conservation district reviews erosion and sediment control above 5,000 square feet. Maryland sets no deadline for deciding a building permit (though since 1 October 2026 the office must decide within 30 days whether a housing application is complete) — St. Mary's County publishes its own targets, and they are the number to plan against.
Rather talk it over?
Call 1-855-478-4290 →Maryland licenses home improvement contractors through the Maryland Home Improvement Commission and home builders register with the Attorney General; trade licences are mostly state licences, but some counties and WSSC license or register trades themselves. Maryland rules
St. Mary's County permit costs and fees
Fees follow the department's published schedule, with review and inspection fees charged by the county and the reviewing agencies the permit is routed to.
| Item | Fee or rule |
|---|---|
| Building permit | Department fee schedule, with fees and processing information published on its site |
| Critical Area | Authorisation and, where the Buffer is disturbed, a Board of Appeals variance |
| Erosion and stormwater | Plans by a professional surveyor or engineer above 5,000 square feet of disturbance |
| Environmental permits | Critical Area and floodplain permits processed by the Permit Services Division |
| Deeds | Recorded deeds back to March 1978 where the property is not in a recorded subdivision |
| Payments | Through the county's own systems only — the county has warned of an email scam requesting review and approval fees |
Pay the county, not the email. The county has published a public notice warning residents of an email scam requesting construction project application review and approval fees. Invoices arriving by email for a St. Mary's permit are worth verifying against the department directly before anything is paid.
Rather not deal with the St. Mary's County building department?
Get a free quote →Trade permits and who may pull them
Permit required
- Critical Area Buffer disturbance — variance approval from the Board of Appeals before the permit
- Electrical — state-licensed master electrician; separate electrical permit
- Plumbing and gas — state-licensed master plumber or gas fitter; separate plumbing and gas permits
- HVACR — state-licensed HVACR contractor; mechanical permit
- Fire protection, alarms and sprinklers — fire marshal review, state or local, with the building permit
Typically exempt
- Like-for-like fixture, receptacle and switch replacement where the licensing boards' rules allow it
- Low-voltage and communications wiring below the local permit threshold
Trade work is permitted separately and inspected locally or, for electrical work in many counties, by a state-certified private inspection agency. Maryland rules
How to apply for a St. Mary's County building permit
Zoning certification, grading and sediment control, stormwater, forest conservation and Critical Area review run ahead of the building permit.
The home builder registration number (required by state law for new homes) or, where the office asks for it, the Maryland Home Improvement Commission licence number goes on the application.
The local application with the building, residential and energy code submittals the scope requires, and trade permits alongside.
Reviewers in the local office check the building, residential and energy codes as the jurisdiction amended them; corrections are answered in writing.
Fees follow the jurisdiction's ordinance and are due before issuance.
Footing to final by permit number, then the use and occupancy certificate that closes the permit.
Review, corrections and what actually causes delay
St. Mary's routes each application to the agencies that must approve it, and the department recommends appointments even though they are not required. What delays a file here is a Critical Area site plan that is not to the county's quality standard, a Buffer disturbance discovered after design, and deeds not produced on an unrecorded parcel.
Want this handled start to finish?
Get a free quote →Inspections in St. Mary's County
Inspections follow the adopted codes' required sequence — footing, foundation, framing, rough trades, insulation and final — and are requested from the local office by permit number. Work that passes final receives a use and occupancy certificate for new buildings and changes of use, or a final approval on the permit for everything else. St. Mary's inspects through the department's inspections division, with its own fax and contact line separate from permits; Critical Area and stormwater compliance are inspected alongside the building work where the plans required them.
St. Mary's County permit search and official resources
- St. Mary's County permits — the Permit Services Division, its hours and its customer assistance guides
- St. Mary's County Critical Area — the authorisation requirement, site plan and Buffer variance
- Maryland Building Performance Standards — the statewide codes the county enforces
- Maryland Building Performance Standards — the statewide code adoptions from the Department of Labor's Building Codes Administration
- Maryland Home Improvement Commission — home improvement contractor licensing and the guaranty fund
- Home Builder Registration Unit — new home builder registration with the Attorney General
Inspections are where schedules slip.
Get a free quote →Frequently asked questions
What needs Critical Area authorisation?
Any development activity — disturbance to land, to natural vegetation, or structural additions and placement — within the Critical Area, with a Critical Area quality site plan filed with the application.
When is a Board of Appeals variance needed?
Disturbance to the Critical Area Buffer routinely requires variance approval from the Board of Appeals.
What triggers engineered plans?
Disturbance of more than 5,000 square feet typically requires an erosion and sediment control plan and a stormwater management plan designed by a professional surveyor or engineer.
When can I file an application?
The offices are open 8:00 am to 5:00 pm, but permit applications are accepted only from 8:30 am to 2:00 pm on Mondays and Thursdays and to 4:30 pm on Tuesdays, Wednesdays and Fridays.
What documents does an unrecorded parcel need?
Recorded deeds dating back to March 1978, plus a contract of sale, lease or notarised permission where the applicant is not the owner.
Which code edition applies?
The 2021 editions of the International Building Code, International Residential Code and International Energy Conservation Code with Maryland modifications, effective statewide on May 29, 2023 under the Maryland Building Performance Standards, with local enforcement required from May 29, 2024.
Simplify St. Mary's County permitting with Alliance Permitting
In St. Mary's the shoreline and the survey decide the project before the code does. We settle the Critical Area authorisation and any Buffer variance before design is fixed, file inside the counter window, and route the plans to every agency the permit needs.
Ready to break ground in St. Mary's County sooner?
Send us the scope and the parcel. We confirm the review path with the St. Mary's County Department of Land Use and Growth Management, assemble the submittal, file it, and track it through issuance — corrections included.
More Maryland permitting guides
More Maryland permitting guides
This guide is provided by Alliance Permitting for general information about St. Mary's County permitting. Requirements, fees, and procedures change; confirm details with the permitting authority before relying on them.