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Counties → Illinois

McHenry County, Illinois

SDWIS compliance plate

Sheet IL111 · McHenry County 307 sys · 11,554 viol · #259/3254

VIOL-SEVERE · HEALTH-LOW · RANK-TOP · PHOTO-FINISH · PFAS-HIGH · SRC-GW · SYS-LARGE · BOOK-FULL

  • VIOL-SEVERE 84.4% flagged
  • HEALTH-LOW 6.3% health
  • RANK-TOP #259/3254
  • PHOTO-FINISH ±0.0 pp
  • PFAS-HIGH 50.0% detect
  • SRC-GW GW lead 98%
  • SYS-LARGE 307 systems
  • BOOK-FULL 7/7 fields

Nearest flagged-rate peer: Kendall County (+ 0 pp flagged-rate)

According to EPA SDWIS county population served used on /counties, McHenry County ranks #259 of 3,254 counties by people served, and #6 of 102 counties in Illinois. See methodology · corpus placement.

McHenry County standing, lower-flagged corpus third

Flagged-system rate 84.4% is at or below the corpus lower third (≤ 92.7% flagged) across 2,973 counties with ≥3 SDWIS systems . Health-based share 6.3% is health-based share at or below the lower third (≤ 10.3%) . UCMR5 detect rate 50.0% is UCMR5 detect rate above the tested-pool upper third (> 33.3%) . Population served ranks #259 of 3,254 · #6 of 102 in Illinois.

Flagged-rate neighbourhood around McHenry County

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

0% 20% 40% 60% 80% 100% Sangamon · lowest McHenry · this county Shelby · near Pulaski · highest 58.8% 84.2% 84.4% 84.4% 84.6% 84.6% 100%

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

Water Systems

System Name Population Violations PFAS
Crystal Lake 40,661 54 Detected
Algonquin 30,700 83 Clean
Lake in the Hills 28,661 52 Clean
Huntley 28,495 84 Clean
Woodstock 25,630 35 Clean
McHenry 22,335 101 Detected
Cary 17,826 66 Detected
Harvard 9,469 79 Clean
Prairie Path Water Co-Whispering Hills 8,300 76 Detected
Marengo 7,572 14 Detected
Fox River Grove 4,702 51 Detected
Lakewood 4,267 242 -
Wonder Lake 3,870 403 Clean
Richmond 2,087 58 -
Wonder Lake (Niu) 1,950 402 -
Aqua Illinois-McHenry Shores 1,862 265 -
Hebron 1,368 11 -
Prairie Path Water Company-Killarney 1,232 27 -
Johnsburg No.2 1,124 157 -
Prairie Grove School 1,050 147 -
Oakbrook Estates MHP 1,012 27 -
Prairie Path Water Company-Holiday Hills 868 19 -
Aqua Illinois-Crystal Clear Water Co. 855 418 -
Prairie Path Water Company-Walk Up Woods 775 27 -
Aqua Illinois-Eastwood Manor 728 309 -
Snap on Tools 700 35 -
IL American-Terra Cotta 681 0 -
Union 594 95 -
Johnsburg JR High School 575 61 -
Spring Grove Elementary School 500 103 -
St Peters Church 500 8 -
Lippold Park Con Softball Boncosky 500 0 -
Aqua Illinois-Nunda 485 194 -
Greenwood School 400 66 -
Illinois Turner Camp Pool 400 26 -
Resurrection Church 350 12 -
Cafe 31 North 300 9 -
Christ the King Church 300 11 -
Valley View School 300 176 -
Northwestern Medicine Woodstock Hospital 300 24 -
Scot Forge 253 68 -
Crystal Creek Farm 251 0 -
Crystal Lake Park D/W Herrick 250 0 -
Shiloh Church 250 96 -
Riverside Pub 220 15 -
Riley Community School 220 87 -
Kingdom Hall of Jehovahs Witnesses 219 2 -
Mary Ann Beebe Ctr/Activity Ctr (18226) 200 27 -
Crystal Lake Montessori 200 193 -
Big Foot Inn 200 8 -

Compare beyond Illinois

Lower-flagged peers for McHenry County

Cross-state counties nearest McHenry County on flagged-system share (84.4%) and cumulative violation count (11,554). 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.