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Counties → Maryland

St. Mary's County, Maryland

SDWIS compliance plate

Sheet MD037 · St. Mary's County 200 sys · 2,495 viol · #497/3254

VIOL-SEVERE · HEALTH-MID · RANK-TOP · ABOVE-PEER · PFAS-CLEAN · SRC-GW · SYS-LARGE · BOOK-FULL

  • VIOL-SEVERE 78.5% flagged
  • HEALTH-MID 32.1% health
  • RANK-TOP #497/3254
  • ABOVE-PEER +1.2 pp
  • PFAS-CLEAN 0.0% detect
  • SRC-GW GW lead 100%
  • SYS-LARGE 200 systems
  • BOOK-FULL 7/7 fields

Nearest flagged-rate peer: Howard County ( -1.2 pp flagged-rate)

According to EPA SDWIS county population served used on /counties, St. Mary's County ranks #497 of 3,254 counties by people served, and #10 of 24 counties in Maryland. See methodology · corpus placement.

St. Mary's County standing, lower-flagged corpus third

Flagged-system rate 78.5% is at or below the corpus lower third (≤ 92.7% flagged) across 2,973 counties with ≥3 SDWIS systems . Health-based share 32.1% is health-based share above the upper third (> 24.5%) . UCMR5 detect rate 0.0% is UCMR5 detect rate at or below the tested-pool lower third (≤ 0.0%) . Population served ranks #497 of 3,254 · #10 of 24 in Maryland.

Flagged-rate neighbourhood around St. Mary's County

Lowest/highest poles plus in-state counties nearest St. Mary's County on % of SDWIS systems with ≥1 violation. Full ladder: /counties.

0% 20% 40% 60% 80% 100% Baltimore city · lowest Howard · near Anne Arundel · near Kent · highest 38.5% 77% 77.3% 78.5% 81.4% 82.1% 96.6%

Source: EPA SDWIS (county aggregates) As of 2026-05-15

Water Systems

System Name Population Violations PFAS
Lexington Park 43,030 31 Clean
Patuxent Naval Air Station (Navfac-Wash) 22,000 164 Clean
Town of Leonardtown 5,000 38 -
Country Lakes 3,016 8 -
Cedar Cove 2,728 5 -
Saint Marys College 2,200 8 -
Chopticon High School 1,845 24 -
Leonardtown High School 1,750 21 -
Wicomico Shores 1,262 18 -
Webster Field Annex, St Inigoes (Navfac) 1,200 37 -
Leonardtown Middle School & Forrest Tech 1,200 22 -
Greenbrier 1,161 5 -
Spring Ridge Middle School 1,075 29 -
Margaret Brent Middle School 1,050 30 -
Breton Bay 1,012 8 -
Lord Calvert Trailer Park 892 45 -
Bradford's Neishyahood Market 818 2 -
Seven Eleven # 21067 Charlotte Hall 805 0 -
Point Lookout State Park North 803 0 -
Hunting Quarters 715 6 -
Rolling Acres 699 5 -
Piney Point 672 9 Clean
Piney Point Elementary School 665 26 -
Lettie Marshall Dent Elementary 650 28 -
St. Clements Shores 620 7 -
Charlotte Hall 615 10 -
Immaculate Conception Roman Cath Chur 614 5 -
Saint Josephs Catholic Church 602 0 -
Benjamin Banneker Elementary School 600 31 -
Hollywood Elementary School 600 25 -
Forrest Farm Subdivision 577 4 -
Laurel Ridge 560 5 -
Persimmon Hills 514 7 -
Wilderness Run 511 9 -
Potomac Speedway 510 3 -
Saint Marys Fairgrounds 502 5 -
Sacred Heart Church 502 0 -
Saint Georges Catholic Church 502 0 -
Oakville Elementary School 475 23 Clean
Patuxent Presbyterian Church 464 0 -
Dynard Elementary School 450 19 -
Hollywood Volunteer Fire Hall 406 7 -
Seven Eleven # 20835 Mechanicsville 403 0 -
Our Lady of the Wayside Church 402 7 -
Saint Francis Xavier Church 402 1 -
Little Flower School 380 58 -
Mechanicsville Elementary 350 22 -
Leonardtown S.h.a./ S.h.a. Maint. 336 1 -
Mount Zion UMC at Laurel Grove 335 7 -
Park Hall Liquors and Deli 330 0 -

Compare beyond Maryland

Lower-flagged peers for St. Mary's County

Cross-state counties nearest St. Mary's County on flagged-system share (78.5%) and cumulative violation count (2,495). In-state neighbours stay on the compliance plate above.

Similar flagged-system rate

Nearest cross-state counties by % of SDWIS systems with at least one violation on record.

4 peers

Similar violation load

Nearest cross-state counties by cumulative SDWIS violation count (all systems in the county).

4 peers

Read our methodology · Check your water system - how this data is sourced, computed, and verified.

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.