Off-grid site report

St. Mary's County, MD

38.2385, -76.5233 · 92 ft elevation

Read this before you act on anything below. This is my researched starting point for St. Mary's County, MD, not legal advice and not a guarantee. Rules change, and the deciding facts on any specific parcel (setbacks, perc results, overlay districts, deed restrictions, road frontage) live at the county or town office, not in any database. Before you buy land or build, confirm the current rules directly with the local zoning and health offices - the sources on this page tell you exactly who to call.

The local rulesSt. Mary's County, MD

Zoning & raw-land occupancy

RestrictedSt. Mary's County has its own countywide Comprehensive Zoning Ordinance administered by the Department of Land Use and Growth Management, including a Rural Preservation District, Resource Conservation Areas, and an Annual Growth Policy capping new dwelling approvals. Raw-land occupancy without an approved dwelling isn't addressed in county sources found. source

Dwellings, tiny homes & RVs

RestrictedThe county zoning ordinance specifically permits mobile homes in certain districts with a building permit, but tiny homes and RV-as-primary-residence outside licensed campgrounds aren't confirmed as permitted dwelling types anywhere I found. source

Building permits & codes

RestrictedBuilding permits are required through the county's Department of Land Use and Growth Management for any structure with plumbing, and the county Health Department reviews water and sewage adequacy, including a required perc test where there's no public water/sewer. source

Septic & composting toilets

RestrictedSeptic systems are permitted locally by the county Health Department's Environmental Health Division under Maryland's state framework; properties outside the 1,000-foot Critical Area buffer no longer need Best Available Technology nitrogen removal as of a 2016 update. Composting toilets are allowed but liquid discharge is separately regulated by the state or local Health Department depending on disposal method. source

Greywater reuse

Varies locallyNo St. Mary's County-specific greywater ordinance was found; the county appears to defer to Maryland's state greywater framework. Not confirmed whether the county Health Department layers on additional guidance, so ask directly.

Rainwater harvesting

Generally allowedNo county-specific restriction on rainwater harvesting was found; Maryland's state environmental site design rule appears to be the operative standard with no county modification confirmed.

Private wells & water rights

Generally allowedThe county Health Department's Well Certification Program certifies potability for new and replacement wells, and most of the county still relies on private wells. Near MetCom water/sewer service areas, some agreements can require eventual connection to public lines, affecting well/septic independence.

Living disconnected from utilities

Unclear - verifyNo dedicated county ordinance addresses full utility disconnection directly; it's shaped indirectly by zoning, building permit water/sewage requirements, and MetCom's mandatory-connection provisions near service lines. Ask the county Land Use department directly for a clear answer on your specific parcel.

Open the full county page with sources →

Sun30-year normals

Peak-sun hours, annual average: 5.0 hrs/day
Worst month (sizes an off-grid array): 3.5 hrs/day
Yearly output per 1 kW of panels: 1,421 kWh

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Weather1991-2020

Precipitation: 47 in/yr
Snowfall: 12 in/yr
Heating degree days: 4,140 (moderate)
Frost-free season: Apr 1 to Nov 12

How far help isstraight-line

Hospital MedStar Saint Mary's Hospital: 7.6 mi
Fire station Second District Volunteer Fire Department and Rescue Squad: 3.4 mi
Hardware store Dyson's Building Center: 1.0 mi
Grocery Weis: 0.1 mi

From OpenStreetMap. Road miles will be longer, often much longer in hill country.

Plan this spot

These open with this location's real numbers already filled in (ZIP 20620).

Size a solar system Heat loss & insulation Firewood per winter Rainwater harvest Garden size Panel tilt

Sources: US Census Bureau geocoder; NLR PVWatts v8 (solar); NOAA NCEI 1991-2020 climate normals (nearest station) or Open-Meteo (ZIP-centroid) for weather; Open-Elevation; OpenStreetMap contributors. Public data retrieved Aug 22, 2026; agencies update their layers on their own schedules. Planning data, not a survey or legal advice.