St. Mary's County, Maryland
26 ZIP codes · Avg score 60/100 · Grade C · Updated 2026-06-04
Safe water is the norm for most of St. Mary's County's 26 ZIP codes — but a notable subset have documented violations that push the grade to the middle tier.
How St. Mary's County Compares
How St. Mary's County Compares
St. Mary's County scores 1 points below the Maryland state average (61/100) and 8 points below the national average (68/100).
Data: EPA SDWIS Last verified: 2026-06-04
ZIP Code Risk Map
Water Quality Map: St. Mary's County, Maryland
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Key Risk Factors
Health risk index: 12.5 (asthma 10.7%, diabetes 11.4%)
Estimated additional annual cost per homeowner: $2,917, driven primarily by sea_level
Infrastructure: 0.337% avg pipe failure probability, 18% of ZIPs at high risk
52.5% of homes built before 1978 (lead paint era)
Violation History (2023–2024)
→ Stable trendEPA violation counts by year across St. Mary's County water systems. Health-based shown in red, total in blue.
Peak year: 2024 with 16 violations. Past 5 years: 18 total (18 health-based).
Source: EPA SDWIS historical violations. Data may lag 6–12 months for the most recent year.
County Health Indicators vs National Average
Black markers indicate national averages. Source: CDC PLACES, Census ACS.
Infrastructure Overview
Sources: Census ACS (housing age), EPA SDWIS (infrastructure risk model), state bridge inspection data.
Compound Risk Breakdown
Estimated additional annual cost per homeowner: $2,917
Bar widths proportional to share of total annual risk cost. Source: compound risk model (FEMA, EPA, USGS).
Housing Age Distribution
35,758 housing units in St. Mary's County
Source: U.S. Census Bureau ACS B25034 (Year Structure Built).
Water Safety Affordability
How much it costs to fix water issues relative to home values in St. Mary's County
Remediation costs are relatively manageable for most homeowners in St. Mary's County, representing a small fraction of property value.
Remediation includes water filtration, lead abatement, radon mitigation, and flood protection where applicable. Source: Census ACS, EPA SDWIS.
Health Outcomes vs National Average
CDC PLACES data for St. Mary's County residents
Black markers = national averages. Red = above national avg. Green = below. Source: CDC PLACES, Census ACS.
Water Systems with Most Violations
Top 5 systems in St. Mary's County ranked by EPA violation count.
| # | Water System | Population | Violations |
|---|---|---|---|
| 1 | Lexington Park | 43,030 | 19 |
| 2 | Patuxent Naval Air Station (navfac-wash) | 22,000 | 13 |
| 3 | TOWN OF LEONARDTOWN | 5,000 | 8 |
| 4 | LORD CALVERT TRAILER PARK | 892 | 8 |
| 5 | Cedar Cove | 2,728 | 8 |
11 total water systems serve St. Mary's County.
All ZIP Codes in St. Mary's County
26 ZIP codes tracked in St. Mary's County.
| # | ZIP Code | City | Safety Score | Grade | Violations | Home Value |
|---|---|---|---|---|---|---|
| 1 | 20636 | Hollywood | 82 | B | 2 | $470K |
| 2 | 20670 | Patuxent River | 80 | B | 3 | — |
| 3 | 20653 | Lexington Park | 77 | B | 3 (1 health) | $342K |
| 4 | 20650 | Leonardtown | 70 | B | 6 (3 health) | $464K |
| 5 | 20606 | Abell | 63 | C | 0 | $464K |
| 6 | 20620 | Callaway | 63 | C | 0 | $369K |
| 7 | 20627 | Compton | 63 | C | 0 | — |
| 8 | 20630 | Drayden | 63 | C | 0 | $585K |
| 9 | 20667 | Park Hall | 63 | C | 0 | — |
| 10 | 20684 | Saint Inigoes | 63 | C | 0 | $376K |
| 11 | 20686 | Saint Marys City | 63 | C | 0 | — |
| 12 | 20692 | Valley Lee | 63 | C | 0 | $382K |
| 13 | 20609 | Avenue | 55 | C | 0 | $475K |
| 14 | 20615 | Broomes Island | 55 | C | 0 | $479K |
| 15 | 20626 | Coltons Point | 55 | C | 0 | — |
| 16 | 20628 | Dameron | 55 | C | 0 | $412K |
| 17 | 20634 | Great Mills | 55 | C | 0 | $335K |
| 18 | 20680 | Ridge | 55 | C | 0 | $392K |
| 19 | 20690 | Tall Timbers | 55 | C | 0 | $559K |
| 20 | 20619 | California | 53 | D | 5 | $364K |
| 21 | 20624 | Clements | 53 | D | 0 | $424K |
| 22 | 20635 | Helen | 53 | D | 0 | — |
| 23 | 20656 | Loveville | 53 | D | 0 | — |
| 24 | 20660 | Morganza | 53 | D | 0 | — |
| 25 | 20674 | Piney Point | 50 | D | 0 | $399K |
| 26 | 20687 | Scotland | 50 | D | 0 | $772K |
Recommended Buyer Guides for St. Mary's County
Editorial-only picks, screened against the EPA detections on file.
- Best Lead Paint Test Kits — 52.5% of homes built before 1978
- Best Under-Sink Reverse Osmosis Systems — Multi-contaminant removal at the kitchen tap
Deep Dive Reports
Detailed analysis for St. Mary's County, Maryland
Overview
St. Mary's County in Maryland covers 26 ZIP codes with an average Home Safety Score of C (60/100).
5 of 26 ZIP codes have recorded EPA violations. 4 health-based violations have been documented.
← Back to Maryland water quality report
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Home values: U.S. Census Bureau ACS (median estimates by ZCTA)
Updated daily.